Living an hour south of the border, my advice is simple:

Relax. If you act like a paranoid, stressed out twit, you'll be treated that way. People don't like being around that kind of person, and it insults your hosts.

You get into a babble about what you think is wrong with our country, and how it would all be better if were Canadian subjects, someone will stuff you in a large garbage can. Seriously.

Remember that the signs are measured in MILES per hour, not kilometers. I've passed people from Quebec doing 40mph (65kph) on the Interstate, they are a hazard.

Our thermometer will read funny to you- don't worry, they agree that fourty below is too cold to go outside.