"We're talking about a homicide," said Gatineau Police Constable Pierre Lanthier at a news conference close to the crime scene.
"Some dead bodies were found inside the residence."
Police weren't saying late Thursday how many people were killed, but had cordoned off an area around 64 rue Felix-Leclerc in Aylmer, across the Ottawa River from the national capital.
A few blocks away, a minivan was parked precariously outside the stately Rivermead Golf Club, its rear hatch opened, exposing piles of children's toys, some luggage and a red plastic gasoline can on top of the heap.
Investigators said the two scenes were linked, although they would not say how.
Police would also not speculate on a motive for the killings or whether it was a case of family violence, but said the man in custody is the prime suspect.
"We will have to interrogate that man," said Lanthier.
"If he is related (to the killings) he might be facing murder charges," he added.
Names of the victims, how many and their ages were being withheld until next of kin could be notified, police said.
The bodies were discovered in the home after a 911 emergency call came in just after the lunch hour Thursday.