Update: Also, almost immediately invalidating my headline, the Jays have acquired Jayson Nix from the Indians for cash considerations. Corey Patterson to the DL. Nix is terrible, but plays/has played 2nd, 3rd and corner outfield.
Just spitballing here, but if I had to guess, this means some combination of the following things:
The club likes Brett Lawrie and thinks he is going to be up sooner than expected, and that he'll be able to play third.
Juan Rivera either is or has become a terrible defensive outfielder, and the club is not prepared to play him in the field (3 year UZR-150: -6.4, 13.8, -24.0)
Edwin Encarnacion has been impressing with the leather.
Jose Bautista really isn't that good of a third baseman after all.
Any of those are possible I suppose, though none of them make a ton of sense individually. I suspect we'll get some sort of non-answer about making guys comfortable or doing the best to win ballgames. More as this develops.