Historically I don't think that's been the case, but I'm not really sure about any past examples of bias..
The broadcasting act says this: The Canadian Broadcasting Corporation, as the national public broadcaster, should provide radio and television services incorporating a wide range of programming that informs, enlightens and entertains.
The rest is details. The board answers to parliment, but parliment consists both an upper and a lower house, only the lower which is what we elect. There is also a governor general, and even a viceroy, and a senate. So the CBC board of governors doesn't answer directly to the party in power, but rather all the elected ministers in government, but also all the senators, and a whole bunch of other weird people with fancy titles.
It's the British theory that once everything is confusing enough and looks silly enough, that people just don't even bother with bias. Sometimes it works, sometimes it doesn't.
The CBC is actually a lot more than just a news station. They have original programming.. and uhh.. a radio station with good classical music, stuff you won't hear anywhere else on the radio.. I'm going to have to be honest and say that I don't really know that much about them - but they do the news right, so every once in a while I'll check out what Mansbridge has to say. I don't think they do hockey anymore, so I haven't really been watching CBC much lately.
Here is the mandate of the CBC btw, if you're curious. It tells them what they're supposed to be doing.
As a taxpayer I support some of my money going to such a thing. It's not a lot of money and we get stuff like Peter Mansbridge out of it. Peter Mansbridge alone would have been enough, but there's
so much more.