It's important to mention that the ballots were redesigned after the 1995 referendum so that the voter's choice is clear and unambiguous. See here:
https://upload.wikimedia.org/wikipedia/commons/thumb/b/bc/2011_ballot.jpg/800px-2011_ballot.jpg
Mark one of the circles only (an X, fill the circle in, whatever), and it's OK. Mark more than one, the ballot is spoiled.
In addition, by law, each citizen gets four continuous hours to vote. That is, somewhere in the twelve hours that the polls are open, your employer has to schedule you so that you can get four uninterrupted hours to vote. So if you local poll open times are 8:30 am - 8:30 pm, and your work schedule is 9:00 am to 6:00 PM, your employer MUST either start your day at 12:30 PM, or end it at 4:30 PM.
In all the voting I've done in Canada, the whole process, from the time I've walked into a polling station to the time I've walked out, has seldom been longer than half and hour and never longer than an hour. No, I've never had to queue outside.