Pros
You have the opportunity to help some of the best and brightest students learn and navigate the university structure. Within my department, there are a lot of new projects being developed, which makes it a very exciting time to be working there. Montreal is an amazing city and McGill's location in the centre of downtown makes it a convenient place to work as well.
Cons
McGill is an enormous bureaucracy with very few people willing to go out of their way to share information or provide assistance to people outside of their departments. Because of this, if you are looking for information from another department, you can get bounced from person to person, or even department to department without ever finding a satisfactory answer. The upper management is not very supportive of lower-level employees and you can definitely make more money at Concordia doing the exact same job.