Suncor said it completed the overhaul. It put roughly 900 people to work on the planned maintenance when it began April 21.
"Suncor's planned maintenance program is designed to support safe, reliable operations," the company said Tuesday. "Production impact has been factored into Suncor's annual guidance."
Suncor's facility in Montreal processes oil into gasoline, heavy fuel oil, and other petroleum products.
Suncor operates three refineries in Canada and one in the United States with a combined processing capacity of 462,000 bpd.
In early April, the company said it plans to spend about eight weeks overhauling its oil sands refinery in Edmonton, Alberta. That refinery is designed to process 142,000 barrels of oil sands per day into light oils.