Pros
CGI is a global operation. Whilst the management frameworks are driven from Canada; the responsibility for bringing it all to life is devolved across the world, along the lines of geography and/or industry. That entrusts significant responsibility to the constituent local Business Units, to provide compelling opportunities for their teams, and to prosper with their clients. Contrary to some of these reviews, I have never found Canada having any desire to meddle at the coal face, unless things were going awry (which is a good thing). CGI isn't for everyone. The whole ethos of the firm is to share an entrepreneurial sprit with your colleagues, help your clients to succeed, and to do so profitably, so that everyone prospers along the way. They're increasingly looking for all rounders who get business, technology, and the 'business of technology/IT services'. When the business model all comes together, you don't need any North American positivity; its self evident in what and how you delivered. A lot of classic brand name IT firms are tanking at the moment; whilst some of the new Silicon Valley upstarts face all sorts of harassment and discrimination charges (age, gender etc.). CGI are good employer.
Cons
The UK is in a period of transition. Many units have embraced the Canadian approach to business, with great results. Others are making slower progress, holding out until forced to do so. Step-by-step, change is inevitable. If you prefer an employee/employer (worker/master) relationship, you probably aren't going to enjoy CGI. Expectation, reward, and self development, is the responsibility of everyone; keeping the business relevant and successful. Once in a Business Unit, if you excel, then its very unlikely that you'll be encouraged to seek opportunities in another one. That is a bit unsettling, but suggest you read the classic Acres of Diamonds, and you'll feel much better!