Yes, yes I have. I've known a lot of Canadians over the decades. They would totally commit to guerilla warfare to defend their nation, same as most other people would. They'd be damned good at it, too.

If you think there's something about Canadians that would stop them from getting down, dirty, and vicious, then you don't know Canadians very well (and have never seen a Canadian hockey game).

Could they hold out alone over the long term? Probably not, but maybe. Smaller, less capable nations have pulled off such feats.

But also, they wouldn't be alone. They'd have quite a lot of support.