On 6 April 2021, Myšák signed a three-year, entry-level contract with the Montreal Canadiens.[7] On 1 October 2021, Myšák was cut from Canadiens' training camp and returned to the Bulldogs.[8] After returning to the Bulldogs, he put up 34 goals and 64 points in 61 games, and four goals and seven assists for 11 points in 17 games in the playoffs. The Bulldogs captured the J. Ross Robertson Cup as champions of the OHL playoffs and moved on to the Memorial Cup. They finished second in the tournament, losing in the final game versus host team Saint John Sea Dogs.[9]
For the 2022–23 season, Myšák was assigned to Laval.[9] However, Myšák's scoring touch from junior level failed to translate in his first season in the AHL, where he scored just nine points in 40 games.[10] During the 2023–24 season, Myšák played in 48 games for Laval, scoring 13 goals and 20 points.[11]
On 7 March 2024, Myšák was traded by the Canadiens to the Anaheim Ducks in exchange for forward Jacob Perreault.[11] He was assigned to Anaheim's AHL affiliate, the San Diego Gulls, following the trade.[12] He played in 14 games with the Gulls, scoring just one goal.[13] The Ducks again assigned Myšák to San Diego to begin the 2024–25 season.[14]
