So to tinker around right now (sorry being a bit of a space case) MLB is looking for 32 teams. Assuming A's relocate to LV I would put my money on the cities most likely to get a team to be Montreal and Oakland. But if Oakland isn't willing to do a stadium deal then I would guess Portland, 1 east coast 1 west coast. This one for ideal build I'm going Portland and Charlotte for ideal builds.
Assume the divisions look a bit like the NFL.
AL East - Yankees, Red Sox, Jays, Orioles
AL North - Twins, Guardians, Tigers, White Sox
AL South - Royals, Texans, Astros, Rays
AL West - A's Portland, Angels, Mariners
NL East - Mets, Nationals, Pirates , Phillies
NL North - Cubs, Cardinals, Reds, Brewers
NL South - Braves, Charlotte, Marlins, Diamondbacks
NL West - Dodgers, Padres, Giants, Rockies
Nothing is perfect about that. I could also see the leagues sliding into 2 divisions like the NHL.