Can-Americans. I don't think the government or the military will have to take over. Like the people coming north from the southern border because things suck where they are, AMericans will invade Canada quietly and take over just in sheer numbers. You can't stop an avalanche.
The more people are in the US and the more they truly wake up and not just IG wake up, the more they're going to get sick of it all, throw their hands up in the air, and walk away with a last, "I'm out!".