Well, okay, so you you think you might (or might not) need a fighter jet, or maybe a drone, or a cruise missle... Here's why you might (or might not) want these things:
Drones are good for when you need to maintain a presence above a section of ground to observe what is going on, and if you have an armed drone, they are great for taking out point targets (people, vehicles, small buildings, etc.) They can stay in the air much longer than a manned air craft, and they don't risk a human going into harm's way.
Drones are NOT good at carrying a large amount of weapons for taking out larger targets (air bases, power plants, radar stations, bridges, etc.) Some of the larger drones are starting to get this capability, so it is logical to assume that this limitation will go away with some of the larger (and more expensive) drones. However, currently drones do not work well unless you control the air space they are flying in. While man-portable surface to air missiles may not have the range to engage a high-flying drone, they would probably be effective against lower-flying drones. Since most current drones do not have much in the way of stealth or counter-measures, they are vulnerable to any surface to air missile that has the range and altitude to reach them. Even old 1960's vintage SA-2's would have little trouble shooting down most drones. Only when you go to very expensive stealth drones do you gain much chance of surviving air space that is protected by even older, cheaper, less-capable SAM's. However, even with a stealth drone, if the enemy has fighter air craft, you are still in trouble. Once the fighter is close enough to see the drone on radar (stealth only reduces the range at which an air craft can be seen with radar, it does not make it 100% invisible), or the drone can be seen with infrared or visually, the fighter has the advantage. Today's drones are unable to dog fight, and the latency and lack of situational awareness that comes from piloting a drone remotely makes them unable to dog fight effectively, even if a drone were made maneuverable enough to even attempt it (which none currently are.)
So, bottom line, drones are useful if you are facing an opponent who does not have fighters, or where their fighters have already been destroyed.
Cruise Missiles are great for hitting fixed targets from long range, like bridges, buildings, military bases, fixed command and control stations, etc. They are not as good at hitting moving targets, as they generally lack the ability to search out and find a mobile target and attack it after they are launched. For the vast majority of cruise missiles, you have to know where the target is when they are launched, and the target can't move while the cruise missile is in flight. This makes cruise missiles largely ineffective against mobile army units (tanks, trucks, infantry, etc.) Army units are the only combatants that can invade territory and hold it, so dealing with them is important. Also, while some cruise missiles can be fired from ground launchers, you can drastically increase the range of cruise missiles if you launch them from a mobile platform like a ship or an air craft. Drones, as of yet, can't carry cruise missiles, so you either need new very large drone, or a manned air craft capable of launching a cruise missile to get enough range to make these weapons effective. The nice thing about a cruise missile is that you can attack well-defended fixed target from a distance without having to risk a human in an air plane, and they are faster and harder to shoot down than a drone.
Conventional Fighter (e.g. a F/A-18E/F Super Hornet)
The Super Hornet is a very versatile air craft. It is capable of both air-to-air as well as air-to-surface combat. If you face an enemy that has fighter air craft, the Super Hornet can try to shoot them down at medium range with missiles, and/or at close range with short-range missiles and a gun (e.g. dog fighting.) In the 1960's, the U.S. thought that missiles were the way of the future and that fighter planes didn't need to dog fight anymore. In the war in Vietnam, they discovered that their missiles didn't work as well as they hoped, and that tactics employed by the North Vietnamese air force meant that it was difficult to avoid getting into dog fights. For example, if you are attacking a military base, and that base is defended by air craft, unless you shoot every single aircraft out of the air from long range fast enough to avoid having your attacking air craft getting withing dog fighting range, you are going to have to deal with defending fighters at close range, which means you need to be able to dog fight. The argument against maintaining this capability is that in a modern war, you can just destroy all of the enemy's air craft on the ground with cruise missiles, and never have to engage them in the air. However, this strategy may not work. Most Russian and Chinese built air craft are designed to operate from rough air fields -- roads, or even flat stretches of grass or dirt, so an enemy can distribute, move, and hide their air craft, making them difficult to hit with cruise missiles (remember when I said cruise missiles don't work well against mobile targets?) Another scenario is if the air craft are based in another country which which you do not want to start a war with (like during the Korean war, when MiG's were based in China, and the U.S. would not attack the air bases in China so as to not risk a war with them) the only way to destroy the enemy air craft is in the air. So, since you can't always deal with an enemy air force with either drones or cruise missiles, you are going to need the capability to engage flying air craft, and history teaches that it is hard to always avoid close-range air to air combat, so you'd better have a fighter that can dog fight.
Assuming you win the air war and gain dominance over the battlefield, a fighter with air to air combat ability becomes less useful, unless it can also operate against ground targets. The Super Hornet is actually pretty good at this, and can carry a useful weapons load of precision guided bombs/missiles, unguided (and cheap) bombs and rockets, missiles that target radars, etc. So, once the air war is largely over, the Super Hornet can start attacking ground targets. However, without something that can effectively deal with enemy air craft, you may never get the chance to attack ground forces, which is ultimately the way you win wars. Turning the tables and looking at defense, the only way to prevent an attacking enemy from taking out your ground forces from long range is to deny them the ability to use their air craft, and that means destroying them (often in the air.) This is why air to air combat ability is so important and needed by any effective air force.
Stealth Fighters (e.g. F-35)
Everything said above about the Super Hornet also applies to the F-35, in terms of why you want a fighter plane that can shoot down other fighter planes, and why it is nice to have a fighter plane that can also drop bombs when the air war is over.
The advantage that the F-35 has over the Super Hornet is all about stealth. Making it harder for your opponent to locate your air craft means a number of things: Your stealth air craft has an easier time shooting down enemy air craft, because you can shoot at them before they even know you are there. If you can shoot at the enemy and they can't shoot at you, that's a huge advantage, and helps you either deny their air craft from access to shooting your ground forces, or allows you to gain access to shoot theirs. Another advantage to stealth is that it allows you to strike at enemy ground targets BEFORE you gain air dominance over their territory. If they can't see you very well, you can strike at their ground forces before you've completely dealt with the enemy air force. That is a significant advantage, and something you don't get as easily with a Super Hornet. However, this capability comes with a hefty price, and that price only makes sense if YOU are the one having to engage the enemy on day one.
So, what does Canada need?
Air defense: Is Canada likely to be invaded? Well, no, and if an enemy force decides to try, Canada will not be going it alone, as the U.S. will step in to help out. Will Canada be invading anyone anytime soon? Probably not. So, what sorts of threats is Canada likely to see?
Well, there is a very large amount of area up north to patrol. Who knows how relations with the Russians might go over the next 30 to 40 years? In the past 30 to 40 years, they've already gone from mortal foe to friendly to sort of strained distance, so who knows? Is Russia likely to field a long range stealth bomber any time soon? Maybe, but advances in radar might keep pace with any developments there, and you don't need a stealth fighter to shoot down a relatively unmaneuverable bomber, whether it is stealthy or not. You need something long range and reliable. The Super Hornet is a better fit than the F-35 here, even though the Super Hornet could use a bit more range. Actually, an F-15 would be a better fit, but I don't know if buying those is on the table. Canada in unlikely to get in a shooting match with another fighter over their own territory, so they really need long-range interceptors. Again, an F-15 would be ideal, but they are more expensive than a Super Hornet. The F-35 isn't that great of a long-range interceptor because it has relatively short range, a small missile load, and only one engine.
The other thing Canada might do is cooperate in a NATO action or some other joint-operation, probably including the U.S. In that scenario, if Canada had stealth fighters, it could participate in the first few hours/days of an air war along side the U.S. If it had Super Hornets, or some other non-stealth air craft, then Canada would have to wait until a country with stealth air craft made the first attacks to degrade the enemy defenses before joining the fight. (This would all depend on how advanced the opponent was.)
It is unlikely that Canada would ever go it alone in some sort of military action involving air craft. So, honestly, the only advantage I can see for Canada buying a stealth air craft is to gain favor with the U.S. by spending more money in the U.S., and by sharing the higher risk of attacking an enemy in the first few days of a war, when the enemy is at its most dangerous. The other advantage would be to have more capability to act with military force without the cooperation of a more capable ally, but does Canada want or need to be able to do that? Canada has few enemies, and what enemies do exist are shared with the U.S. and Europe.
Others have complained that the Super Hornet is older technology and would be need to be replaced sooner than an F-35. Well, yes and no. The airframe is based on a design from the 1970's, but it has been updated, improved, and is made from more modern materials in many places. Also, the laws of aerodynamics really don't change, so the only disadvantages to an older air frame is efficiency and fatigue life. Since the Super Hornet would be newly built, as would the F-35, there is no advantage to either plane in terms of fatigue life -- they will both start new and slowly wear out to the point they need to be replaced or repaired. In terms of efficiency, the Super Hornet is actually better than the F-35. The F-35 has quite a number of compromises made to it's shape in the name of stealth. The F-35 is slower, less maneuverable, and can't carry as large a weapon load as the Super Hornet. The F-35 has a longer range on internal fuel, but the Super Hornet can carry more fuel in drop-tanks to compensate. So, there's no real advantage there, either. The electronics in the F-35 are more advanced, and this gives the F-35 more capability in certain scenarios than the Super Hornet, but electronics can be upgraded, often much more cheaply than buying a new plane. In fact, the biggest long-term obsolescence risk is actually with the F-35's stealth technology. If Russia or China makes a more advanced radar than can better detect the F-35, than the major advantage of the F-35 is nullified (at least for well equipped opponents.) The stealth features of the F-35 isn't something you can easily upgrade later, because it is built into the structure of the air craft. When advances in radar technology make the main advantage of the F-35 less of an advantage, what are you left with? A plane that really isn't that much better than the Super Hornet, at twice the cost.
The F-35 will have significant capability advantages over well-equipped opponents compared with the Super Hornet for probably the next 20 years or so. After that, the differences between these two planes in terms of capability will be largely down to which air craft is getting a radar upgrade and better electronics. Is that 20 year advantage worth the cost? For Canada, and their needs, I don't think so. For the U.S.? Maybe.