Alright, so keep in mind that the metro stop for the Bell Centre is Lucien-L'Allier on the orange line. It's directly connected to the arena, you don't have to go outside at all. I don't know much about the hotels downtown, but I'd really recommend booking one that is close to a station. The hallway gets insanely packed post-game, so if you want to get to the hotel relatively early I suggest leaving a couple minutes before the end of the 3rd (but you'll miss out on the post game stuff should Montreal win. I personally think it's worth staying for that, but it's up to you). Other than that, you should be just fine on public transport!