The move was made prior to Tuesday's midnight deadline but announced by the Habs on Wednesday. NHL rosters are frozen through midnight, Dec. 27, although players can be recalled from the minors at any time.
The 21-year-old had three goals and an assist and was plus-5 in four games since he was brought up to the NHL club on Dec. 11.
Should centre Steve Begin return from a back injury as expected on Thursday, the Canadiens would have needed to send a player down because they would be over the 23-man roster limit.
Lapierre does not have to clear waivers when returned to the minors. The Montreal native was expected to be in the Bulldogs' lineup for a game against the Manitoba Moose in Winnipeg on Wednesday night.
Lapierre, a second-round draft pick in 2003, played one game for Montreal last season and did not get a point.