I'm not a betting man by nature, and there'd be no way to settle the bet even if I proffered it, but I'm sure that:
a) the Pentagon does have contingency plans in place for the scenario you described, and
b) they're highly classified, in large part because the Wonkette circuit would go moonbat-feral if those plans ever were declassified.
By all means, keep up with the thought experiments. Like many others here, I find them fascinating. If I have any skin in the game, it would be as a welcomer if patriots have to seek refuge in Canada a la It Can't Happen Here. The gun laws in the Great White North are almost shockingly restrictive - we Canadians are actually forbidden to own any sort of AK-47, period - but Canada's peaceable, the riots are few and they tend to be cracked down upon.
I’m thinking from your Pierre T. example, that it might have been similar to the often-cited case of conservative (?) president Nixon opening China. A democrat would not do so, for fear of inviting the criticism of being in bed with Communists.
So perhaps a leftist Trudeau is more free to unleash hell upon the lefties? A conservative might have had more hesitation. That’s something to consider. Perhaps a Democrat president might be the first to issue shoot-to-kill orders against “his own people.”
How ya fixed for Enfields?