I think the fact that CBC is even considered Canadian culture is a problem of it's own. The government's effort to protect Canadian culture inevitably leads to the government defining what Canadian culture is. It's very phony. Culture comes from the people.
I would argue against the statement that American culture is supplanting Canadian culture, but only because I would say Canadians have always consumed American culture more than Canadian culture. Talented Canadian artists have always made their money in America. Even the 'elbows up' movement was started on an American television show by a Canadian who made his career in the US.
I think an honest assessment would be that Canadian culture and American culture are very similar. They have always been related. We were both largely colonized by Brits. We are neighbors. There are, of course, things which are distinctly Canadian. But I would also say the fact that Canadians have always consumed American culture is reflective of Canadian culture. I mean this is what actual Canadian people decide to do, as opposed to what the CRTC tries to promote that we do.
The government puts too much effort into being Canadian. If you are something, you don't have to try very hard to be it. Also, I think so much of that effort is focused on the idea of not being American.