Grant, 27, spent the 2015-16 season with the Arizona Coyotes organization, recording 11 goals and 31 assists for 42 points in 69 AHL games with the Springfield Falcons. He finished second among AHL defensemen in shots on goal (180) and tied for second in power-play points (24).
Grant also skated in five NHL games with the Coyotes last season.
A native of Antigonish, N.S., Grant has skated in 323 regular-season games in the AHL, recording 43 goals and 131 assists for 174 points with Springfield, Binghamton, Norfolk and Wilkes-Barre/Scranton.
Originally a fourth-round pick by Pittsburgh in the 2007 NHL Entry Draft, Grant has two goals in seven career NHL contests.
Casto, 24, completed his third AHL season in 2015-16 and set career highs in goals (7), assists (16) and points (23) in 68 games with Providence. The native of Stillwater, Minn., has totaled 11 goals and 35 assists for 46 points along with a plus-25 rating in 186 career AHL games, all with the Bruins.
Casto has also skated in 20 Calder Cup Playoff games, totaling three assists.
Ferlin, 24, produced six goals and eight assists for 14 points in 23 games with Providence last season. Over his two pro campaigns, he has 17 goals and 17 assists for 34 points in 76 contests.
Ferlin, a fourth-round draft pick by Boston in 2011 and native of Jacksonville, Fla., recorded one assist in seven NHL games with the Bruins in 2014-15.