True, Canada military is crap. But isn't Canada too difficult to invade because of its vast geography?
Also, Canada has allies. Maybe they wouldn't fight, but would provide weaponry. It would be too much of a long drawn out war that would cost too much money for the US.
10 Countries that might provide aid according to this dude. He is actually implying they would send troops: Denmark, Netherlands, Germany, France, Australia, UK, Norway, South Korea, Spain, Sweden.