Pros
The best reasons to work for IBM Canada especially early in your career is that it is a great way to learn a lot about many different things. Of course this is true of any system integrator/management consultancy where you have the opportunity to work on multiple projects for different clients. IBM is a world leader in many areas and of course there are some extremely talented people.
Cons
IBM is not an environment for talented people who think outside-of-the-box and focus on company success above matrix politics. There are a lot of line managers who are so enmeshed in IBM politics and group think that they have completely lost sight of the company mission. Risk taking of virtually any kind is universally frowned upon. This is a very top heavy, bureaucratic institution and a lot of well connected and extraordinarily incompetent people rise while talented visionaries walk.