Montreal's health authority says 11 people have now died from complications related to the hot and humid weather.
Another four deaths have been reported in the Eastern Townships region east of Montreal, with officials expected to provide an update later today.
Meanwhile, the ambulance service that serves a large swath of the Montreal area is calling on people to refrain from calling unless it is a real emergency.
Urgences-sante says it has been inundated by the volume of calls since a heat wave enveloping Eastern and Central Canada settled in for an extended stay over the weekend.
The ambulance corporation says it has received 1,200 calls per day in Montreal and nearby Laval over the past four days, which is 30 per cent more than on usual busy days.
Urgences-sante president Nicola D'Ulisse says the service is overwhelmed and has reached the limits of what it can provide.
He is asking residents to call a provincial health-consultation line in the event of minor health problems or to check in with friends or family and leave 911 lines free for real emergencies.
Environment Canada says a heat warning remains in effect for an area spanning southwestern and northeastern Ontario through southern Quebec and into the Atlantic region, with above normal temperatures and humid conditions likely to stick around into Thursday.