^ Your classification of superpower status is mainly based on military power. In which case the USA and Russia win because they got more bombs. But civilizations are not all centred around military power. Diplomacy, Economy, Culture, Technology and various other aspects are all important. Canada didn't have a "cold war" with anyone because they chose to emphasize on other aspects of civilization. Rather than building more bombs Canada chose to fund free health care for all of it's citizens. Again, Canada is amongst the world leaders in all of the above, save military might. That's what I'm getting at.
Yes, but the USA kicks Canada's ass in pretty much all categories EXCEPT healthcare. Denmark's got a great healthcare system too, but it's not in civ. Let's go through your criteria one by one:
Diplomacy - Not an experienced diplomatic historian, so I'll improvise for this one. Diplomacy is based largely on how much the nation matters to the world stage - why people try to strike bargains with North Korea and not, say, Ghana. Canada's played the diplomatic game well, but that alone doesn't qualify them for anything.
Economy - Correct me if I'm wrong, but the US dollar still has a higher value than the Canadian dollar (despite its recent economic pants-crap). And who managed to drag down the entire world when they had an economic crisis? The US. Now, that doesn't qualify them for a "good leadership" award, but it does qualify them for importance.
Culture - This one's easy. Hollywood's in California, not Quebec. Canada didn't invent Rock 'n' Roll - choose one: Elvis or Celine Dion. Guess which one was American? McDonalds has an outpost in almost every country in the world - got a Canadian restaurant with the same cache? Y'know those cowboy movies the whole world is so enamored of... guess where cowboys come from? Wanna know how many of the top ten grossing movies of all time are from the US... all of them. (though in all fairness, LotR was filmed in New Zealand) The top one hundred... all of them. Yeah, Canada can suck it.
Technology - Not sure on this one because I bet you can name a thousand small things that canadians invented. But... atom bomb? Internet? Electric guitar? Hell,
electricity? Yeah, US got this one too.
All of these things can be pinned on the fact that the US has a larger population than canada. In answer... what, you want Culture
per capita or something? That's just silly. In conclusion, I repeat that Canada can suck it.
Disclaimer: I actually really like Canada. But the phrase "Canada can suck it" rings far too much to exclude it.