Casualty #4: Dominic Canzone
This one should seem obvious when you think about it. Canzone has great power potential, and could get a nice return still in a move, having improved his value since the Mariners got him from Arizona last season, even if only by a little bit.
Here's why he is likely gone. The Mariners have a platoon that they like in left with Raley+Robles. Julio is in center. Locklear+France+Garver locks up the DH spot. That leaves RF as the position to go and improve via trade, and turns Canzone into a piece that they should be looking to move.
Would Canzone+prospect(s) net you a big OF? I think so. Or you could move him for an impact relief pitcher (with some other parts attached to one side or the other), possibly an Adam Ottavino style who brings a vastly different type of arm to the Mariners bullpen. Teams love homers, and Canzone has great power. Teams would likely take that gamble on him to hope he figures out the average side of things, and the Mariners could capitalize on it.