I grew up in Winnipeg, MB Canada. I lived in the north east of England near Newcastle and now live near New York City and have done for about 15 years. So, as the Brits would say (and some Canucks too) I am an ex-patriot Canadian - a Canuck without a country.
I think it is always dangerous to make generalizations, but I believe that there might be a few points one might make regarding the differences between Canadians and Americans.
First - I believe Candians have a more socialistic view of their world. I am not saying this is better, but a fact dictated by the different political systems. In America, there is much more focus on the individual - for example individual rights be paramount and superceeding almost all else, whereas Canadians seem more willing to sacfrifice some of there personal freedoms for what they believe to be the better good of all. This I think leads to personallity differences, whereas Americans will be more outward and self-assured, Candians tend to be more willing to conform. Of course, there are exceptions, and I find myself being one, perhaps due to living close to New York City for quite some time!
But mostly I believe that because Canadians find it difficult to describe themselves in some way that is distinct from Americans there exists a certain level of the feeling of inferiority. The USA has about 10 times the economy and people that Canada does and a lot of what goes on in Cnada is deictated by the pressures of the American economy. This for the most part is fine, but is akin to a mouse sleeping with an elephant. All is fine until the elephant rolls over in its sleep, (whether it actually planned to or not). I believe that this is the reason that Canadians find it diffcult to make a distinction. I would, however point out that one, naturally perhaps, assumes that eveything "North American" is American first. I would therefore turn the question around and ask the Americans to describe something that is American that is not also Canadian !
Such a few thoughts from an ex-pat Canuck !