I think the Jays have a fairly solid D, but I'm not sure I'd call it top-5. Our outfield D looks great - Vernon is a gold glover, both Rios and Reed can cover a lot of ground and have good arms.
On the IF, I think we're still a bit shaky - Hill is getting better and showing range, but he still has 3 errors already this year. Clayton has looked solid if unspectacular. I agree that Overbay is a good defensive 1B and Glaus looks pretty good - still wouldn't say he's a top-10 defensive 3B. I think Zaun is great at handling the pitching staff but isn't a top defensive C - has only thrown out around 23% of base stealers the last couple years.
Haven't given it too much thought, but I'd think there are definitely NL teams with better D (Mets, Marlins, Cards plus lots more) and there must be AL teams too (Angels and Tigers come to mind, but again I haven't thought it through).
If Overbay were to go down, I highly doubt that Thomas would play 1B - I don't think he's played in the field since about 2004 and there's no reason to move him out of his DH spot. Stairs, Smith and Phillips all played some 1B last year, so I'd assume that one of them would fill in.
Mulliniks Watch: Still stuck on 1325 games 3569 AB 445 R 972 H 73 HR 435 RBI 0.272 AVG 15 SB