The film, with the original Sami title "Garrat du Váimmu", is about 20-year-old Ejva, who finds herself in the middle of a love drama between her boss and his cousin after she is forced to take over the family reindeer when her father dies.
Kernell has previously directed the Guldbagge-winning films "Sameblood" and "Charter".
"I look forward to the world meeting this fantastic cast, which basically consists only of reindeer herders," she says in a press release.
"Make the Heart Hard" has been selected for the festival's competition section Platform, where it is competing for a jury prize.
Also competing in the same category is London-based Swedish artist and filmmaker Bertil Nilsson with his first feature film, the British-produced "Masc".
The Toronto Film Festival, one of the most important in North America, opens on Sept. 10.
