Khmer, Ethopia, Vietnam, the Dutch, Portugese, Mayans, Byzantines, Sumerians, Babylonians, Siam. They all have vibrant histories, and have had an impact on either their region, or even the entire world.
So what about Canada? Mounties? Celine Dion? No thanks.
As fun as it would be to play as my home country, I could probably think of a good 50 others that I'd want to see in the game first. The United States represents North American civilization pretty well already, whereas areas like Southeast Asia and Oceania are painfully underrepresented.
If I may, I'd like to use a real-world argument I heard a few months back from a historian on CSPAN re: why America and Canada are viewed differently in terms of impact on the world. I think it implies well to Civilization too. This isn't an anti-Canada post, but rather an explanation of why two seemingly similar nations are not judged the same in regards to the history of civilization. I apologize in advance for the paraphrasing, but this was the gist the argument:
America is influential on the world's historical stage because it was able to forge a unique and (at the time) innovative cultural identity that Canada could not. World history has a good idea of what it is to be "American" or to have the "American dream": a nation built upon the idea of democratic innovation, multiculturalism, and the desire to rise from an impoverished immigrant to a prosperous "American." While Canada also holds the ideals, they never capitalized on them culturally, as America did. They never encapusated a "Canadian dream" or shown the world what it is to be a "Canadian."
Basically, although America's sister colonies of Canada and Australia went on to become great countries, they have not had the impact on general civilization as America has. I think when Firaxis decides which civs to include in the game, one of the major criteria that they consider is the civ's impact on civilization as a whole, and how history changed because of them (good or bad). Canada is just not there yet.
As a Canadian, I think what you cited is fairly misleading.
You think that Canada does not have a strong democratic value, or more liberal idealism?
You think the immigrants to Canada don't have a dream? I am an immigrant, and I like Canada. I have tons of immigrant friends, coming from different parts of the planet, they all love here.
Multiculturalism? Stop kidding. Canada is WAY more culturally tolerant. As a Chinese, I feel like myself in Canada. I lived in US for over a year, and I had to be like an American at that time.
So instead of claiming the US for being more able to capitalize "culturally", I'd rather attribute it to the stronger economy of US when compared to Canada. I don't care how horrible a big-Mac tastes (OK...one big-Mac is fine with me, try a few in a week, it tastes like xxxx), by putting enough money to hardsell it and package it, it will "taste good". Make it simple, the so-called American "culture" is basically 95% a product of commericalization and aggressive marketing supported by strong funding.
Then you may challenge, why do the Americans do a better job in economy than the Canadians? Doesn't it imply superior cultural value, or superior education system, or superior whatever in the US? As a Chinese, I don't find much "culture" in the US. As a post-doc when living in the US, from what I saw IMHO an average American college student is not as knowledgeable and smart as an average Canadian student at similar level.
What it basically comes down to is the US occupied a stretch of land with better weather and more readily available resources (and the much larger population and thus a bigger market as a result). Say one day God (or whatever, just fill in the blank) freezes half of your land. I'd really want to see how culturally vibrant you guys will become.