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.