He just has to come to terms on a contract, Comcast Sports Net New England reported, citing industry sources. Red Sox bench coach DeMarlo Hale had been one of the finalists but was told earlier Friday that he was out of the running, Boston radio station WEEI reported.
Former Indians catcher and current coach Sandy Alomar Jr. was also reportedly a finalist for the position.
Gaston retired at the end of the season after his second stint on the Blue Jays bench.
Farrell, 48, pitched for the Indians, Angels and Tigers from 1987-96. He worked in player development with the Indians from 2001-05 before becoming the Red Sox pitching coach. Farrell and manager Terry Francona were Indians teammates.
The Blue Jays finished fourth in the AL East this past season with an 85-77 mark.