Primeau, 22, has compiled a 1-7-1 record in 11 games with Montreal this year, along with a 4.88 goals-against average and a .866 save percentage.
He also made 16 appearances with the Rocket this season, posting an 8-6-1 record, along with a 2.77 goals-against average, a .912 save percentage, and two shutouts.
The Northeastern University product was a seventh-round selection of the Canadiens (199th overall) in the 2017 NHL Draft.
Hammond, meanwhile, was acquired from the Minnesota Wild earlier in the day.