If Brady did not retire, I would have predicted Tampa Bay - he's the sort of guy who (prior to last year) got open enough for Brady to take full advantage of.
Ideally he would want to go to a contender with cap space and a vacancy for his skill set. If Saquon Barkley does leave them, maybe the Giants?
They will let Saquon walk if he doesn't come to his senses, but the Giants would be a great landing spot for him regardless. They have the cap room as long as they don't do something stupid like give Daniel Jones $45 Million a year but no real skill players on offense.