The Whitehorse, YT forward joined the Canadian Sport School Hockey League (CSSHL) for the 2020/21 U15 Prep season. The following season he would play in the U18 Prep division as an underage player, posting a division best 42 assists and 65 points in 35 games with RHA Kelowna. The Medicine Hat Tigers would then select McKenna with the first pick at the 2022 WHL Draft.
During the 2022/23 U18 Prep season with South Alberta Hockey Academy McKenna would lead the league with 37 goals, 38 assists and 75 points while being named the CSSHL U18 Prep MVP. That season McKenna would play 16 games with Medicine Hat tallying 18 points.
McKenna joined the Tigers full time for the 2023/24 season, posting 97 points in 61 games as he was named the WHL and CHL Rookie of the Year, a WHL (Central) First Team All-Star, a CHL All Rookie Team member, and a CHL Third Team All Star. He would also represent Canada Red U17 and Team Canada U18, posting a total of 28 points in 14 games. He would be named a U17 World Hockey Challenge All Star, and a U18 World Junior Championships Gold Medalist, All Star, and Top 3 Player on his team, leading the event with 10 goals.
In 2024/25 McKenna posted 129 points and a WHL best 88 assists in 56 games as he was named WHL and CHL Player of the Year, and a CHL and WHL (East) First Team All-Star. He would add 38 points in 16 playoff games as Medicine Hat were crowned WHL Champions before heading to the Memorial Cup where McKenna was named to the Memorial Cup All Star Team. McKenna would represent Team Canada at the World Juniors, posting 1 point in 5 games.
This past season McKenna joined Penn State University, posting 51 points in 35 NCAA games. He would add 14 points in 7 World Junior games with Team Canada, capturing a bronze medal. McKenna was named to the NCAA (B1G) All Rookie Team, NCAA (B1G) Second All Star Team, the NCAA (B1G) Rookie of the Year and Scoring Champion, and a NCAA (West) Second Team All-American,
McKenna is the second CSSHL alumni to be selected first overall at an NHL Entry Draft, joining former North Shore Warriors star Connor Bedard (2023 – Chicago Blackhawks)
