The event was supposed to happen on Thursday prior to the game between the two teams that night.
Officials at Honoré-Mercier Elementary School canceled the event after a parent complained that an 11-year-old girl was asked to remove her Bobby Orr Bruins jersey on a prior Canadiens jersey day.
"She's been a Boston Bruins fan all her life, so she kinda felt really bad. She felt kind of excluded from the school," her father, Tony Pasquale, told CBC News.
Pasquale did not make the complaint himself and he was critical of the decision to cancel. "It teaches respect, sportsmanship. We can't all be from the same thread," he said.
English Montreal School Board spokesman Mike Cohen defended the school's decision.
"We don't think it's prudent for a student to wear a Boston Bruins jersey in a school during this very intensive playoff play," Cohen said. "At this stage in the game, with the Canadiens leading the series 2-1, why ignite things, why create a controversy?"
Unfortunately for the administrators at Honoré-Mercier Elementary School, the Bruins won Thursday night's game 1-0 in overtime and the series is now tied up at two games apiece.
Game 5 will be on Saturday night in Boston.