Ontario Provincial Police were called to the scene just before 11 p.m. ET on Saturday, and found that a westbound pickup truck had collided with an eastbound commercial vehicle.
The driver of the commercial vehicle and the occupants of the pickup were all killed in crash, but police say none of their identities has been confirmed.
Two other commercial vehicles were damaged in the collision, but no one else was hurt.
Highway 17 between Upsala and Ignace re-opened Sunday morning, after closing overnight for the investigation.
Anyone with information is asked to call provincial police in Thunder Bay at 807-939-2133 or 1-888-310-1122.