Can't see Giannis accepting the supermax deal that he is eligible for this offseason, unless he just really really like the city if Milwaukee.
Either the Bucks trade him to get a head start on an impending rebuild, or they make a coach change/ trade some players and picks and go for it in Giannis' final year.
Mavs would be a very attractive option of Giannis is okay with sharing the spotlight alongside Doncic. Doncic is a playmaker who can create also shoot from the perimeter. Porzingis, when healthy, is a good stretch 5 that would spread the floor and doesn't clog up the paint.
Warriors depending on their cap situation would be nice as well. Curry and Klay are older and might be okay with taking a back seat to Giannis. Giannis would step into a situation where he is the #1 guy but still has guys like Curry and Klay on the perimeter helping him out.