Montreal health officials are blaming the heavy heat and humidity for at least six deaths in recent days.
Dr. Mylene Drouin told a news conference today the deaths have been investigated and are linked directly to the heat wave.
Drouin says the victims fit the profile of people authorities describe as at risk: those with chronic illness or mental-health problems, people who live alone and people without air conditioning at home.
She says there has also been a rise in the number of calls to ambulance services in recent days and that the city wants to avoid what happened in 2010, when intense heat claimed 106 lives.
The oppressive weather has enveloped much of Central and Eastern Canada since the Canada Day long weekend.
Environment Canada says humidex readings will be in the 40 Celsius range today from southwestern and northeastern Ontario through southern Quebec and into the Atlantic region.
The weather agency says a "very warm and humid air mass" has settled over the Maritimes and above normal temperatures and humid conditions will stick around into Thursday. Maritime temperatures are expected to return to seasonal normals for the weekend.
A hot and humid air mass is also entrenched over southern Quebec, with Tuesday's highs expected to be in the low 30s with a humidex reading between 35 and 40 through, also through Thursday.
Southern Quebec was rocked by violent storms on Monday, leaving thousands of homes and businesses without electricity, or air conditioning. Most of the outages were in the Outaouais region of western Quebec in addition to area north and northeast of Montreal.
Environment Canada said much of southern Ontario, including Toronto, also remains under a heat warning, with a humidex reading of 43 expected on Tuesday. The extreme heat was expected to ease off on Friday with the passage of a cold front.
Advocates in Toronto will be handing out water at Margaret's Drop In at 323 Dundas St East, as the city and shelter workers try to help vulnerable people during the city's heat wave.
Flooding possible in Alberta
In western Alberta, meanwhile, the problem is rain and lots of it.
As of late Monday, about 30 millimetres of rain had fallen in the Jasper region, creating the possibility of flooding in low-lying areas. Environment Canada said another 25 to 50 millimetres of rain were expected before it tapers off Wednesday morning.