Yusei Kikuchi is another Blue Jays starter to consider, a free agent at the end of the season. Not great, but would give the Red Sox some SP depth. Obviously, the key piece/acquisition would be Guererro.
Gausman is interesting in that he has been a quality starter in the past but is having a down year. Can the Red Sox figure out a way to get more out of him? The Blue Jays would probably like to move on from Gausman, since he will make 23 million next year and 23 million in 2026. Taking on Gausman would probably reduce Guererro's trade value since the Blue Jays would like to dump the contract. Bassitt is the more attractive SP option for Boston--he is having a better year than Gausman and is only signed for one more season.
Teel, Lugo, Jordan, and Romero for Guererro, Bassitt, and a relief pitcher?
The cheaper route for the Red Sox would be Teel, Lugo, Jordan, and Romero for Guererro, Kikuchi (free agent at the end of the season), and a relief pitcher.
It is hard to know which Blue Jays starter would be most appealing to Breslow. He seems to have particular preferences, but I don't know what they are.