Kiwi, what the posters have said so far is for the most part correct. Outwardly there is very little difference between Americans and Canadians. We look alike; we pretty much enjoy the same foods. Canadians may be a bit more into hockey, Americans a bit more into football. But other than that, there is no significant difference.
However, there is a profound difference in outlook. Canadians have been members of the Commonwealth, subjects of the monarch for a long time now. Canadians are more respectful of authority than Americans are.
There is a standing joke. How do you get 50 Canadians out of a swimming pool? You say to them ‘OK guys, everybody out of the pool’. Canadians respect authority, institutions such as parliament, courts etc. much more than Americans do.
Canadians are not subject to the kind of Bible thumping patriotism that sells so well in USA. Religious right, while very strong in USA (they have almost taken over the Republican Party) are fairly weak in Canada (they are one of the many interest groups that make up the Conservative Party).
In general, Canadians are much more liberal than Americans. In most of the issues such as abortion, death penalty, gun control, gay rights etc. Canadians are very liberal, tolerant; Americans tend to be much more conservative.
Indeed, I have said it many times, if Obama were to run in Canada, he would have to run as the leader of the Conservative party, and I wouldn’t vote for him. He is too conservative for my taste.
So superficially there are very few differences. However, if you look deeper, you will find profound differences.