Not only that, I really don't understand the doomsday attitude, like a few years of Seager means Vlad can't EVER play 3b again.
An upgrade is an upgrade. If Vlad has good hands and instincts, he'll probably be just as valuable at first (see Matt Olson, who was largely average at the plate but still put up over 3 WAR) and if and when Seager leaves, he can always return to third.
Segura + Seager, Keuchel and a few key pitching upgrades in the BP (where there are tons of great FA options) makes the Jays a pretty dangerous team.