Police commander Dacid Vijakainen warned residents to avoid using generators and barbeques to heat their homes after a 52-year-old man and his 72-year-old mother died northeast of Toronto.
Police in Quebec said carbon monoxide poisoning is believed to be the cause of three deaths in a chalet on the province's North Shore.
In Toronto yesterday night, 11 people were taken to hospitals with signs of carbon monoxide poisoning. Mayor Rob Ford said the city received about six times as many calls about carbon monoxide yesterday about 110 over 24 hours as it gets in a usual day.
Officials said 90,000 customers in Toronto were still without power, down from 300,000 people at the height of the outages over the weekend. Officials said some may not have power restored until after Christmas.
In Quebec, fewer than 32,000 customers remained without power as of early today. In New Brunswick, more than 47,000 customers were still in the dark.
Travelers trying to get home for the holidays continued to face delays and cancellations on airlines and trains.