Who Takes Professor X's Chair?

Sir Patrick Stewart, who died this week at 86, played Charles Xavier for twenty-six years, and his final turn arrives in Avengers: Doomsday on December 18. Nobody replaces him. But someday Marvel will need the older Xavier, so who takes the chair? Ralph Fiennes, Stanley Tucci (already Marvel as Dr. Erskine) or Jason Isaacs, the fan-cast Magneto who's already captained a starship? Cast one, cut one, give one a callback. Cast, Cut, Callback is a series from Box Office Ballot.