Ideally for only 1 of Stroman or Sanchez, a quality bullpen arm (Santos or Janssen) and one other player (a replaceable major leaguer or a non-elite prospect)
That probably doesn't get it done I realize, since Scherzer > Fister
The fact he's a Boras client and therefore likely unextendable will mean teams almost certainly won't give up 2 elite prospects for him