Toronto police said it happened on McCowan Road and Milner Avenue, north of Highway 401.
When police arrived, they located four people with gunshot wounds.
Toronto rescuers said one male victim suffered serious life-threatening injuries, two male victims were seriously injured and a fourth man was slightly injured.
No suspicious information has been provided.
It is the fourth shot in the city on Sunday.  Earlier this afternoon, four people, including two boys, were seriously injured in three separate shootings over a two-hour period.
Police also did not release any suspicious information about these incidents.