Pros
CGI is one of the biggest technology consulting firms in the world. There's nearly limitless career possibilities, many different ladders to climb, skills to learn. Great for self-starters who want to forge their own path, explore their interests, and build a long career. Especially well suited to technologists with interests across the business spectrum (marketing, sales, operations, etc.). It's also heavily invested in SAFe (Scaled Agile Framework) and offers lots of opportunities for training and certifications, which is either a pro or a con depending on your appetite for agile frameworks. Same goes for cloud, it's a great place if you want to grow skills, get certified in AWS & Azure.
Cons
Not necessarily a cons, but a words of caution. CGI is not a software product company (at least for now, it would certainly love to change that). It is built around enterprise-scale IT projects, managed IT services, and IT strategy consulting. If you are a hardcore software engineer and are not interested in developing broader business consulting skills, you will likely find your career ladder to be short and feel undervalued. At CGI *everyone* is called to be a consultant. It's part of the culture and you aren't going to change that. You also won't see the kind of money being thrown at you like you would at a SaaS/PaaS/IaaS company. CGI values time in the trenches, so you won't start seeing big checks unless you stick around a few years, and start impacting revenue. Also CGI has some interesting policies around limited middle management which is both a pro and a con. There's only allowed to be like 4 or 5 people between anyone and the CEO, and there are rules about how many people management roles should manage, which severely limits the number of roles. Breaking into the Manager/Director level and above can be challenging, often requiring good internal connections and good timing.