There is a the ptoential for Boston, New York, and Cleveland to end up with identical records when the season ends on Sunday. I know that means there would be a play-off between New York ad Boston on Monday, but would there then be a play-off on Tuesday with loser and Cleveland on Tuesday?
The loser of the Yankees-Red Sox playoff would play the Indians. From an article by Christian Ruzich on Baseball Prospectus that deals with this type of situation (substitute Indians for Mariners):
While that may have been the official scenario in a part year I can’t actually find what MLB plans to do this year. The MLB “what if?” page doesn’t address the OP’s scenario.
That page also covers what happens if the AL East and the AL Central end in ties. That’s a nightmare scenario which could potentially result in 3 playoff games just to determine the AL playoff teams.