A Canadian friend just experienced this, too. He had many years with the same employer and was recently fired for nebulous reasons and offered a paltry severance package. He's currently in the process of suing. I do not know _anything_ about Canadian labor laws but I did find it _very_ interesting that he went through this experience as a Canadian with a Canadian company in Canada (BC). It goes against everything that I thought that I knew about the treatment of workers there (no surprises there, of course, as I am a naive person, but still...).
They don't have to, no. But I've been laid off, and given two weeks pay in lieu of notice, and I appreciated it. I don't have to give two weeks notice, either. But those who enjoy receiving courtesy should also give it.
This is why I never feel bad for quitting a job without giving the expected two week notice. They don't give you any notice when they fire you.