Pros
There are offices everywhere so many people have the option to relocate. When your company gets acquired, they let you keep your same salary, and there's good benefits and 401k match.
Cons
You go from a small firm of having high status to suddenly being the small step child. There are too many hands in the pot and everyone thinks the other person will take care of it. Theres a ton of miscommunication. Theres the fear of things changing dramatically from the great benefits you had at the small firm to now going by the rule book of Stantec. Lets see, I get blocked on the internet trying to access sites that I need to do my job all the time... that's fun. You lose a lot of the culture that you had when you were a small company, mostly because a ton of employees will jump ship quickly after being acquired.