I don't know, Montreal is more than massive enough to have zero trouble finding an ownership group/person for an NBA team.
Case in point:
NBA | Le projet de franchise à Montréal stagne
It's in French but that's already a group who's been working on getting a team. With that said, the leader of that group says that the NBA will be more interested in Seattle and Vegas before anyone else.
Regarding an arena, not sure how it would work with Molson but in essence, they'd already have a perfect downtown arena for the team. The language thing is fully a non-issue. It's a dying issue (particularly among the young) and a Montreal NBA team wouldn't have the cultural baggage that the Habs/hockey does. Just like with MLS/CFL (and AFAIK, the Expos), I think just about the entire city would expect the player demographics/language to resemble the rest of the league.
As for the climate. Well...NYC, Boston, Philadelphia, Detroit, Toronto, Minnesota, etc. etc. all have teams. Not sure I see the stake there. I think a lot of players would be more worried about what their shoe deal would look like being based in Canada as opposed to the US but with a globalizing world, hopefully that gap can be bridged.