What chance does Montreal have in acquiring an American League expansion franchise?

No Chance

MLB isn't expanding anytime soon. Its already stretched to the point where the smaller market teams don't compete well with the big markets.

Even if the MLB expands its highly unlikely that Montreal will get a team - They've had a team and failed to support it. Toronto pretty much gets the support (and revenue) from most of the Canadian market so there's no business case for a 2nd Canadian team.

Portland, Charlotte and Montreal are the undisputed favorites, though Portland would be the logical fit in the AL for a natural rivalry with the Mariners. Vancouver is another name I hear, but obviously they'd do one West one East, so I don't think they're the threat to Montreal that Charlotte would be. Very few are myopic enough to bring up the Expos in any of this so it would strictly be a contest of who can deliver the best package when the time comes. I see Portland and Montreal as the favorites, IMO, without getting into heavy specifics.

Zero. Montreal failed miserably to support the Expos. And there are no plans I am aware of for an expansion of either league.

They may get another chance because territory in the USA is gone, and Mexico City will never get a team or want a team because of what the USA did to them in the big war before WW1.

Probably not a good chance because it did not have good attendance before. That is why it lost it's team before. There may be other cities ahead of it.

It would make sense for MLB to add an expansion team in each league -- or add two in the AL and return Houston to the NL -- and Montreal and Las Vegas are cities that are being mentioned right now.

Montreal may be a hard sell, however, because of the pitiful attendance figures the Expos had over their last seven seasons there. Stade Olympique was jumping for two Mets-Blue Jays exhibition games in March but an expansion team may have trouble holding the fans' interest.

Portland, OR has drafted blueprints for a baseball-only stadium in the hopes that MLB will consider it if and when it decides to expand, and they may be a viable option if MLB passes on Montreal.

Expansion is currently not planned.