Police were dispatched to the complex at 65 Old Burnhamthorpe Rd., near Mill Road and Burnhamthorpe Road, just before 7 p.m. after receiving a 911 call for a stabbing.
Toronto police Insp. Tim Crone said a family member arrived home and discovered the three victims.
The initial investigation led police to identify a suspect and locate him in a nearby ravine in the area.
"There was a brief standoff with the suspect — he was armed (with a knife)," said Crone, noting that "tensions were high."
"Officers did a very good job calming the situation, calming the individual and got him to come into custody without incident," he said.
Police said they haven't confirmed the identification of the three victims and aren't able to comment on any relationship the deceased may have to one another.
"It's still very early in the investigation," said Crone. "Homicide has taken over as the lead investigators for the scene."