Actually your wrong, its gets warmer than 21 Celsius in Alberta even in the northern parts...I know because I live in Alberta and even last summer we had stretches of 30C+ for a week or two...if you don't think so just search the historical records :-)

It was warm enough I had to keep my AC running all day and could only turn off after the sun went down and even then inside the house remains at 20-22 C during the night.

Perhaps the times you visited it happened to be cooler but I can assure you summer does indeed get hotter that 70F...though I realize you made a typo and said 70C.

Without confirming my location I am considered to be in Northern Alberta and for sure its cooler than southern AB but its sure the hell is not 21C all summer and thats more the average, it gets hotter :-)