Pros
CGI is a growing company with interesting projects and most groups (but not all) are good to work in. They put a lot of energy into creating a good culture and corporate accountability, although this is not pushed into all groups very effectively.
Cons
I can't speak to all parts of CGI globally, but in the US, people are treated as disposable. Some groups are very dysfunctional and it's tough to get management or HR attention to fix the issues. Also, in the US, the bench policy is only 3 weeks so if you end up without a project, you have a very short timeline to find one. If you don't find one within that period, you're fired, no matter how many years you have been with the company. I have seen 20+ year veterans land on the bench and get terminated - and there's nothing that their manager can even do about it. They don't even lay you off with an option to come back when there is work - they just fire you. There is no mandate to prefer internal candidates, so even if you're a high performer with great skills, if you're too expensive or not exactly the right fit for a project (even if you could do the job), the hiring project doesn't have to take you. This is a waste of talent when they are hiring with one hand and letting good people go with the other. It's tough to say it's a good company when there is so little loyalty to their long-term employees.