The crash occurred in Caledon on Highway 10, just south of Forks of the Credit Road.
Police believe that a northbound GMC pickup truck entered the southbound lanes of Highway 10 and struck a Honda Odyssey minivan.
Two people died at the scene. Seven others were taken to hospital.
On Sunday afternoon, the OPP identified the deceased as Christopher White, 49, of Halton, and Elizabeth McDougall, 41, of Mississauga.
White was driving the van that was hit, while McDougall was a passenger. Another 41-year-old passenger remains in critical condition at Toronto's Sunnybrook Health Sciences Centre.
According to police, the 24-year-old male driver of the pickup truck is in serious condition at St. Michael's Hospital in Toronto.
Police have previously reported that the man was the only person in his vehicle when it struck the van, which was carrying eight occupants.