The accident happened Wednesday in snowy and icy conditions on a stretch of highway through the La Verendrye wildlife reserve in Quebec's Abitibi-Temiscamingue region about 350 kilometres northwest of Montreal.
Four members of the same family from Longueuil, near Montreal, were killed in the crash.
Quebec provincial police identified them on Thursday as Danny Lambert, 36, Stephanie Lavallee, 29, Mya Lambert-Duchesne, 7, and two-year-old Emy-Rose Lambert.
Sgt. Marc Tessier of the Quebec provincial police said investigators believe Lambert's car went out of control before it hit the oncoming truck.
"The preliminary investigation indicates the driver lost control of his vehicle as he executed a passing manoeuvre," he said. "It's an area where you're not able to pass so if it's snowy and icy....
"The investigation is not concluded. We still have witnesses to interview."
Snowbanks lined the road, making it narrower.
The impact of the collision split the car in half.
The driver of the truck suffered several injuries and was transported to hospital although police do not fear for his life.