To defend against Trump? Last time America tried to invade Canada, it went badly. If Trump tries again, it will go badly again, for different reasons.
The US spends 916B per year on its military. Canada, 27B. But it's even worse than that sounds, because *Canada does not have a military designed to function independently*. On many key capabilities it is either grossly deficient or lacks them entirely, as it's premised on defense with allies. Namely, the US.
Let's ignore for now the US's >3,7k nukes. The Canadian air force has 258 aircraft, mostly older vintages.
Not combat aircraft- total.
Most of Canada's combat power is 85 CF-18 Hornets. Mostly the original, dated A version.
The USAF has ~5500 aircraft. Fighters alone, ~1300. This isn't counting army or navy aviation! Of the most advanced, the US has 188 active F-22s and 553 F-35s. Putting a F-18 A up against either is a joke. It's not even a fight.
Canada would lose air superiority basically instantly.
When one side has air superiority in modern warfare, they can basically flatten whatever they want at will and rain down as much air support as they want when they come under fire. Conventional warfare has its days steeply numbered once air superiority is established.
Which leaves unconventional warfare. Guerilla warfare. Great. But it doesn't appear in a vacuum. Effective guerella campaigns, esp. in the modern era, aren't "some guy in a cabin with a hunting rifle". They require training, organization, and most of all, preparation.
Which Canada has not done.
You're simply living in a fantasy if you think Canada can militarily even slow the US down or put much more than a minor thorn in its side if the US decides to invade.
I'm not saying this because I *want* it to be the case. I VERY much don't. I say it because it *IS* the case. And in particular, I say it so you don't cling to ungrounded fantasies, and get down to the cold hard reality of *actually investing*, immeditely, in starting to build up a credible deterrence, independent of the US.
This means a Finnish-style "total defense" at home, & an "Article 5" with the EU.