Rogers will be paying $20M for Martin, a declining vet, in a rebuilding year when there are others who can and really should replace. $20M is sunk cost.
If they trade him and eat $16M, they come out of 2019 $4M ahead of the game, and (presumably) Martin gets to play for a contender, and maybe even be the everyday catcher.
The Jays get 1-2 prospects (the more the FO eats of that contract, the more and higher quality prospects we get) and an extra young player gets to stay up in the MLB and get some experience.
The Jays will not be an absolute tire fire unless Sanchez and Stroman suck again. Nothing Martin can do about those two sucking, other than framing, etc., and by many measurable many of the Jays in the system offer decent defense. So that gap won't be that significant. Play the kids, see what we have, and if one or more fizzle, address subsequently by trade or FA signing.
$4M better off with prospects? Oh yeah, the FO will be taking a look at that scenario.