a few other differences, like having a parliamentary system of government, and being a member of the British Commonwealth. I think you're overly diminishing the role of geography, too...nowhere in the US do people feel the need to clump together near a border to stay warm.

And, ahem, slavery remained legal in the Empire until the Slavery Abolition Act of 1833. There would have been slaves in Canada, but the real difference is that they never were integral to a major swath of the Canadian economy.

Of all the differences I can cite, I think the form of government is the one that's most significant. It might be hard to prove scientifically that a parliamentary system works better, but the contrast you're drawing between Canada and the US is that Canada more reliably produces results like other parliamentary democracies, notably the European ones.

Canada's the European nation we wish we could become.