I know that Brett Gardner is very popular with Yankee fans but he's really an average player for a starter. Stanton replacing Gardner is a massive upgrade. I'm guessing the Yankees would look to trade Gardener but he'd be great 4th outfielder if they kept him. He's a good defensive player who can play all three positions adequately, is a decent batter, and would make for a very good pinch runner in late inning situations.
I’m assuming Clint Frazier will be included in the package of young players shipped to the Marlins. That leaves Hicks, Ellsbury, and Gardner, one to start in center, one to be the fourth outfielder, and one to go elsewhere.