Both are good schools in their specific regions.You need to evaluate based on your post-MBA goals.Factor that you need to consider are your location of choice post the program (you want to work in Asia or North America) and if there are any specific industries or roles you are looking at (in that case check which region has more opportunities in your field of interest).
NUS MBA is a higher ranked program which you probably already know.
I don’t know anything about NUS, but McGill is one of the top universities in Canada and Canada has pretty good universities.
What is your citizenship?
Without the guarantee of good job and PR visa, studying a generic garbage major like MBA is a waste of money and time.