Actually, canada has a rather small and unadvanced army, in a few hours, the national guard would be fighting, we'd have air support from the begining, canada is friendly to the US, and if we, for some reason, couldn't beat them, we'd nuke them. Then almost any american with any weapon whatsoever would be trying to fight back, shotguns, rifles, knives, bow and arrows, etc. Canada would get their arses handed to them on a silver platter by US citizens alone with makeshift weapons. There are more cows in the US than canadians, so we could overrun them with cows jk