If you're going to attend a game in the largest NHL arena, you will want great seats on the lower level because the sight lines on the upper level aren't all that great, especially in the 400s.
I have been coming to Canadiens games for years, at least 3 games per season and I always love sitting in the Habs' attack zone. It always seems to be where to most passionate fans and they seem to always cheer the loudest.

Not until you sit in the corners do you appreciate the athleticism of some of these guys with all of the beating they put on each other. They're strong, fast and big. Get the double lettered rows in 117 if you can; rows AA-FF, those are the closest to the glass. Single lettered rows are great too.