Canada is larger than the United States.
And America is hardly "more" diverse. I don't have Bell Canada here either, and they are on the forefront of trying to implement caps. I'm sure there are also only a handful of big players in the market that control it in the US.
And yes, there are caps. But for the moment we have stopped them from forcing independent (all the smaller providers) ISPs to implement the same ridiculous caps and charges. Thus, there are still options available for unlimited bandwidth.