Sano is going to sink or swim based on his bat, and his health, not his prowess with the glove at third. If he stays healthy, and hits, he'll be at third most days. If he doesn't hit, or can't stay healthy, first base matters not. Cruz/Austin/Cron won't stand in his way, either way. And unless there's a prospect I don't know about, there's nobody in the minors that will push Sano off third either, for quite some time. So it's Sano or Adrianza at third, or possibly Schoop if Gordon suddenly remembers how to hit.