2014

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. He next competed at the Pacific Rim Championships where he once again helped Canada win the bronze medal.^[2]

In August Cournoyer competed at the 2014 Youth Olympics in Nanjing, China.^[3] While there he placed 19th in the all-around during qualifications and was the first reserve for the final. He did qualify to the vault and horizontal bar finals. During event finals Cournoyer placed sixth on vault and seventh on horizontal bar.^[1]

2015–16

Cournoyer was selected to make his senior international debut at the 2015 Pan American Games in Toronto.^[1] While there he helped the Canadian team finish fourth; individually he placed eleventh in the all-around and seventh on pommel horse. Cournoyer next competed at the 2015 World Championships where he helped Canada finish 15th during qualifications.

At the 2016 Olympic Test Event, Cournoyer helped Canada finish eighth as a team; unfortunately Canada was unable to earn a team berth to the 2016 Olympic Games.

2017–18

In May 2017 Cournoyer competed at the World Challenge Cups in Koper and Osijek. Later that summer he competed at the 2017 Summer Universiade where he finished 11th in the all-around.^[4]

Cournoyer was selected to represent Canada at the 2018 Commonwealth Games alongside Cory Paterson, Jackson Payne, Scott Morgan, and Zachary Clay. Together they won silver behind England.^[5] Individually he placed seventh in the all-around, sixth on horizontal bar, and fourth on rings, vault, and parallel bars.^[1] Cournoyer competed at the 2018 Pan American Championships where he won silver in the all-around behind Manrique Larduet of Cuba.^[6]

At the 2018 World Championships Cournoyer helped Canada finish 18th during qualifications. Individually he finished 23rd during qualifications which qualified him to the all-around final; however he withdrew due to an injury to his abdominal muscle.^[1]

2019

Cournoyer competed at the 2019 Pan American Games alongside Zachary Clay, Justin Karstadt, Cory Paterson, and Samuel Zakutney. Together they won bronze as a team behind Brazil and the United States.^[1]

At the 2019 World Championships Cournoyer helped Canada finish 17th during qualifications and individually he finished 43rd in the all-around during qualifications. Although Canada did not qualify a team to the 2020 Olympic Games, Cournoyer qualified as an individual due to being the highest placing Canadian athlete and being one of the top finishing all-around not part of a qualified team.^[7]

2020–21

In early 2020 Cournoyer competed at the American Cup where he finished tenth.^[8] This would be Cournoyer's only competition of the year due to many events, including the Olympic Games, being postponed or canceled due to the global COVID-19 pandemic.

In 2021 Cournoyer competed at the Olympic Games. He finished 55th in the all-around during qualifications.^[9][10]

2022–23

Cournoyer was selected to represent Canada at the 2022 Commonwealth Games alongside Félix Dolci, Mathys Jalbert, Chris Kaji, and Jayson Rampersad.^[11] However, prior to competition Cournoyer tore his ACL.^[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. During qualifications he helped Canada finish fourth, which qualified Canada a team berth to the 2024 Olympic Games, a feat last achieved by the Canadian men's gymnastics team in 2008.^[13] Additionally he qualified to the all-around final. During the team final Cournoyer contributed scores on all six apparatuses towards Canada's seventh place finish. During the all-around final he finished twelfth.^[14]

Cournoyer next competed at the Pan American Games. On the first day of competition he helped the Canadian team win the silver medal behind the United States.^[15] Additionally he qualified to the floor exercise, rings, and horizontal bar finals. On the first day of event finals he placed seventh on floor exercise and sixth on rings. On the final day he won bronze on horizontal bar behind Brazilians Arthur Mariano and Bernardo Miranda.^[16]