[1] Cournoyer made his international debut at the 2014 Junior Pan American Championships where he helped Canada finish third as a team and individually he won gold on floor exercise and silver on vault.

[1] While there he helped the Canadian team finish fourth; individually he placed eleventh in the all-around and seventh on pommel horse.

[4] Cournoyer was selected to represent Canada at the 2018 Commonwealth Games alongside Cory Paterson, Jackson Payne, Scott Morgan, and Zachary Clay.

[1] Cournoyer competed at the 2018 Pan American Championships where he won silver in the all-around behind Manrique Larduet of Cuba.

[1] Cournoyer competed at the 2019 Pan American Games alongside Zachary Clay, Justin Karstadt, Cory Paterson, and Samuel Zakutney.

[9][10] Cournoyer was selected to represent Canada at the 2022 Commonwealth Games alongside Félix Dolci, Mathys Jalbert, Chris Kaji, and Jayson Rampersad.

[12] Cournoyer was able to make a comeback the following year and was selected to compete at the 2023 World Championships alongside Zachary Clay, Félix Dolci, William Emard, and Jayson Rampersad.

[16] In late June Cournoyer was named to the team to represent Canada at the 2024 Summer Olympics alongside Zachary Clay, Félix Dolci, William Émard, and Samuel Zakutney.