Completely different political parties, official languages (one has 2, the other has none), histories, the nature of the people in the countries, namely Canada is a collage, while the USA is a melting pot. The USA has far more people, and no "empty" land left, except perhaps in Alaska, while 85% of Canada is Crown Land, i.e., empty. Canada has more lakes - more than the rest of the world combined. The USA has a much larger military.
And, and, and. There are actually a lot of differences.