To me this depends entirely on the cost. If the Marlins are holding out for a 2022 Sandy return, then it doesn't make sense, but if the Jays can get him at a more reasonable cost, then to me it's a no brainer. He's the SP to get. Not only is he controllable beyond 2025, but I think there's a strong chance he finishes the year strong. Stuff+ and Location+ are both good, and on the Jays he'd have elite defense behind him and probably the best defensive catching/framing tandem in the league. The alternatives are buying high on Ryan (if he's even available), Cabrera, Keller, etc, and giving up way more prospect capital.
With the way the Jays have prioritized extra rest and low pitch counts for the geezers in the rotation this season, I think running a 6 man rotation is probably something they not only wouldn't mind doing but might be planning on as well. The last time they had a shot at the division at this point in the season was 2016, where they acquired a struggling Francisco Liriano and went with a 6 man rotation down the stretch.