Pros
Certain units have very high standards and hold their employees to them. Others are just places where so-so IT consultants stagnate. Try to find a gem of a manager; it makes life at CGI a lot nicer.
Cons
The company's different units spend a lot of time and resources figuring out how to shift costs around so nothing hits their books. This is an IT consulting firm that branches out, mostly through acquisitions, into business consulting. If you're not from an IT background, you won't get much respect. And even if you are...this is a technology company with regular email failures and a "helpdesk" that is uniquely unhelpful. Over the last several years, the benefits have gone from fine to barely acceptable. They took away a week of vacation from new hires, for instance. Raises and promotions are few and far between, even for strong performers.