I'm a U.S.?
While both Alan Dillman and Scott Young are correct about the passport requirement, it's actually a bit more draconian than they think. Since shortly after 9/11, not only do you need a passport to get back in to the USA, but by law it is illegal for American citizens to leave the USA without valid documentation to return. What I'm saying is that even if Canada had no requirements, you would still need your passport or EDL when you leave the USA.