I genuinely doubt that. Manufacturing consent for war has always been necessary for Americans, and while that's easy when the target is some non-white country far away and especially when it's a country there's been decades of propaganda leveled against, trying to flip a switch against a country that white supremacist Americans see as human and which right up until that moment have been allies seems a lot harder to sell.

Preemptively attacking their own allies for literally no reason except they felt like it would fracture the American public in ways that terror bombing an uncooperative periphery state couldn't. The US would become a pariah state and quite possibly even start seeing internal guerilla warfare from Canadians and Canadian sympathizers. Might even start getting troop rebellions as soldiers find their conscience when told to murder other racist white people who speak English instead of scary brown people who do not.

Which is why they should do it. Just completely obliterate the empire in the most unforced error of all time.