Police who arrived at the scene about 10:30 a.m. EDT found a hunting shotgun was found next to the body of the gunman, the Canadian Broadcasting Corp. reported. Investigators were working to determine whether he died of a self-inflicted wound.
The body of the day-care worker was found in another building at the same day-care facility, the CBC said.
The names of the two men had not been released, the network said.
Gatineau Police Chief Mario Harel told reporters at a news conference the shooting may have stemmed from the recent breakup of a relationship. He said police were summoned to the day-care center, where a man was said to be threatening people.
The 53 children and other staff at the center, registered as Les Racines de vie Montessori, were taken to a neighbor's house until parents arrived, the CBC said.