The passage of a cold front along with a 30 per cent chance of rain on Friday is expected to help temper the heat, leading to more seasonable summer weather the following weekend.
They planned to visit thousands more as the heat was expected to continue until Friday.
The adopted criteria includes a daytime temperature of 29 degrees Celsius or higher and nighttime temperature of 16 degrees or higher or a humidex of 36 degrees Celsius or higher.
Overnight low temperatures in the high teens will some relief from the extreme heat.
Heat warnings were also in place for New Brunswick, P.E.I and Nova Scotia, where similarly intense conditions could push the humidex close to 40 on Thursday.
A cold front passed through the region Monday afternoon, but we'll still have to wait a few days before the sweltering heat dies down, said Weiqing Zhang, meteorologist with Environment Canada.
The heat is hanging in there but take heart - it was a mere 18 C at dawn Tuesday and daytime highs will stay in the 20s by Friday.
It says "a very warm and humid airmass" will settle over eastern Quebec and the Maritime provinces this weekend, and will last into next week.
The national weather agency says humidex values will climb back up to 40 C or higher on Wednesday and Thursday. The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors. "And also do not forget to make sure you don't leave any people or pets in your vehicle, as temperatures will rise dramatically within minutes".
There are many warning signs for heat illness, including swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some health conditions.