Environment Canada issued heat warnings for four provinces on Tuesday, including Ontario, Manitoba, Saskatchewan and Quebec.
Temperatures could reach 30 C in parts of northwestern and northeastern Ontario, with humidity making it feel closer to the mid-30s, Environment Canada said, with similar conditions expected in southwestern and southeastern Ontario.
The City of Toronto will keep seven public pools open until around midnight Tuesday to help residents cool off during the heat advisory.
Heat advisories remain in effect for parts of northern Manitoba, where wildfires have prompted additional air quality advisories due to smoke.
Environment Canada has also issued an air quality statement for the area around Lytton, British Columbia, where a large wildfire has grown to 20 square kilometres.
Meanwhile, parts of southern Manitoba could see strong thunderstorms on Tuesday, potentially creating suitable conditions for tornadoes, Environment Canada said.
Some communities across the province experienced record temperatures over the weekend.
Dominion City, which is about 80 kilometers south of Winnipeg, had its hottest July 17 on record with temperatures reaching 34.2 C, surpassing the previous record of 32.2 C set in 1942.
McCreary, located about 200 kilometers northwest of Winnipeg, also set a record for the day with temperatures of 31.9 C, surpassing the record of 31.7 C set last year.
Shoal Lake, about 250 kilometers west of Winnipeg, recorded temperatures of 31.2 C. Its previous record for July 17 was 30.9 C in 2011.
In Saskatchewan, heat warnings are largely limited to central and northern areas of the province, with daytime temperatures expected to hover around 30 C, Environment Canada says.
Parts of Saskatchewan experienced periods of extreme weather including hail, heavy rain and intense lightning on Sunday.
Heavy rain overnight Monday also caused flooding in parts of Regina.
The heat and humidity can make parts of southern Quebec feel like 40 C or more.
A cold front moving across the province could also bring showers and thunderstorms.
Across the pond, temperatures hit record highs in the UK, breaking 40C for the first time.
In Spain and Portugal, the heat wave led to nearly 750 deaths, while wildfires broke out in those countries and elsewhere in Europe.
With files from CTV News, The Canadian Press and The Associated Press
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