Gabrielle and Jacob Rondeau were asleep when their 17-year-old brother left them alone in the apartment on Marengere Road to get pizza with his girlfriend, he told Radio-Canada.
Daniel Rondeau said firefighters were battling smoke and flames when he returned around 11 p.m. ET.
The twins were unconscious when they were rescued from their second-floor apartment.
The fire started in the kitchen, the Gatineau fire department said.
More than 20 people were forced out of the four-unit building during the fire.