Last time I flew into YUL there were so damn many people in the pen that they wouldn't even let people down the stairs because about 3 massive airliners all landed at the same time. Easily 500+ people in line -- took me over an hour and I nearly missed my flight. Nexus queue length: 0. One experience isn't definitive one way or the other, but the way I see it, Nexus can't hurt, but not having one can :P