The Northeast US also buys a lot of power from Canada, so you'll be drinking radioactive water in the dark while the fallout drifts over. Having fun yet?
Oh by the way since the lights are out, you might have to deal with riots in cities like Baltimore...lots of Americans in the 99% who will use unrest to their advantage
Anywho, this is all sci-fi...most of Canada is barren and not worth invading. It's not clear what invading it would even get you.