Would you be willing to part with Adam Lind and roll with Juan as your everyday DH? I don't think I would be willing to, but I do think Lind would have significant trade value.
Francisco might provide 80% or more of the offense that Lind does and that night be an acceptable sacrifice. (Power vs OBP) But he might not.
Also, although I might get ridiculed for this - Lind feels like he should remain part of this team if they're playoff bound. After all his years here (he's the most tenured guy on the roster if I'm not mistaken) it would he a shame if the Jays made the playoffs and he didn't get to be part of it.
That said, if I could get a legit SP upgrade for a package of Sanchez, Lind, and another prospect I still might do it. My reservation would be more the Francisco risk than the loyalty thing.