Shakti Ramsurrun was arrested near the scene without a struggle on Thursday.
He was with his 15-month-old son at the time. The child has been placed in protective child custody services.
The victims were identified as Louise Leboeuf, 63, her partner Claude Levesque, 58, and her daughter Anne-Catherine Powers, 21.
Ramsurrun and Powers were the parents of the toddler. While the couple were reported to be estranged, Ramsurrun was still living in the home at the time of the deaths.
Police said Ramsurrun had only been a legal resident of Canada since December.
Gatineau police Const. Pierre Lanthier said the victims were killed Thursday with a sharp weapon. The bodies have been sent to Montreal for autopsies.
The suspect was arrested outside the stately Rivermead Golf Club, where police say he worked.
The club is near the victims' home in Aylmer, a bedroom community just across the Ottawa River from the capital.