The solution is not very simple, and is mostly contingent upon what the Mariners do at second base and/or center field. Basically, will Dee Gordon be on the roster in 2019? If the answer is “yes,” then Robinson Cano will likely become their full-time first baseman. If not, it’ll be Ryon Healy.
To make things more interesting, let’s say Gordon stays on the team and slots in at second base. Of course, this is also contingent upon the Mariners filling their hole in center field in free agency (but we’ll talk about that at a later time *wink*).