Pros
Generally the company is well organized on the HR front. Decent (not great) benefits. Average Pay. There are good opportunities for the 'right' people. Stantec has the ability to grab high profile projects due to it's diversified service offerings. If you happen to be on one of those projects, then life is grand at Stantec.
Cons
Engineering consulting firms are, in my opinion, crappy places for engineers to work. Better to seek out work from the consulting firm's customers - even if the pay is lower, the job security and work opportunities are better. Stantec stands to lose a lot of business as they are not integrating their PC's rapidly enough. As other reviewers have pointed out, the Profit Centre organizational model is killing their business and puts up walls between offices that don't need to exist. Also, as other reviewers have noted, shortly after acquisition, mostly younger managers put in high positions - I would have preferred to see some older people with some wisdom and patience running the show. Also you are expected to get your own work as a PM, which is not entirely a bad thing. I found their rates to be too high for many customers and could be potentially pricing themselves out of certain markets.