I think the Canadian living in the US that you responded to was close to the mark. Most Americans have little contact with Canadians and many think of Canada abstractly, but not very accurately, as a European-like country located above the US. Beyond this abstract idea, most Americans don't have any reason to think about Canada on a regular basis.

Also, Canadians may not think of themselves as Americans, but young Anglo-Canadians are products of American culture. I roomed in college with one for a year and nothing was distinctly non-American about him besides the accent.