To start his first full professional season in 2021, McCann was assigned to the Double A Midland RockHounds, where he hit .166 over 93 games at both first base and catcher. In 2022, he spent most of the season at Midland but also appeared in 7 games for the Triple-A Las Vegas Aviators. He hit 21 home runs while batting .234 for the season across both teams. In 2023, McCann was a non-roster invitee to the team's spring training. During that time, observers noted that McCann had significantly improved from the prior season, with the San Francisco Chronicle calling McCann "the A's most improved player in spring training."[7] He was believed to be the most likely back-up catcher on the main roster before being leapfrogged during the final week of spring training by veteran Carlos Perez.[10] He subsequently played the entire season in Las Vegas, hitting .270 with 17 home runs in 97 games. Defensively, he played primarily at catcher (60 games) while making 10 appearances at first base. He also appeared in 27 games at designated hitter. He spent much of the year sharing catching duties with top prospect Tyler Soderstrom.
Major leagues
In 2024, McCann was again a non-roster invitee to the spring training roster competing for a back-up spot behind Shea Langeliers. On March 28, the Athletics selected his contract and added him to their Opening Day roster.[11] In his MLB debut on March 30, McCann went 0-for-2 in four plate appearances, walking twice. He also drove in a run and struck out twice.[12]