More than 85 firefighters responded to the call on Laurendeau Street. The fire was finally extinguished by 6 a.m.
It caused significant damage to the three-storey commercial and residential building.
Montreal Fire Operations Chief Michel Girard said it appears the fire, which started on the stairs and roof of the building's garage, was intentionally set.
"Certain people told us they heard explosions before the start of the fire," he said. "When firefighters arrived, the fire was burning at a good intensity."
Montreal police said their investigators were brought in after firefighters deemed it suspicious.