The only constant to the last 150 years of Canadian life has been how not-American we are. They are treasonous colonials who hate the British crown, while we dedicate 24-hour news coverage to Prince George learning to use a toilet. They waged brutal, genocidal war on their native inhabitants, while we were civilized, and made ours sign treaties before starving them onto reserves. They're still working out how not to have police murder black people in the streets for no reason, while we have a gender-equal cabinet and more Sikhs in government than the Republic of India. Like Batman and the Joker, we genuinely need each other in some strange, tragic way. An American diaspora on the Canadian shield would really mess with our sense of self.
But then again, this would also be the most liberal set of Americans -- those who are most aspirationally Canadian, the ones already convinced that public healthcare, firearm restrictions, and early morning Caesars are the way, the truth, and the life (respectively). All things considered, we could probably deal.