Toronto Marlies

On April 4, 2019, Brazeau signed an AHL contract with the Toronto Marlies.^[2] However, he would only play one game for the team in the 2019-20 season, instead playing most of his games with the Newfoundland Growlers of the ECHL. After registering 27 goals and 55 points in 57 points, his season came to an early end on March 12, 2020 as the ECHL season was postponed and later cancelled due to the COVID-19 pandemic. On April 2, 2020, Brazeau was named to the ECHL's all-rookie team.^[3]

Brazeau made the Marlies out of camp for the delayed and shortened 2020–21 season.^[4] However, Brazeau had troubled adjusting to the AHL, only scoring four goals for five points in 21 games with the Marlies.

Boston Bruins

Brazeau signed an AHL contract with the Providence Bruins in 2021.^[5]

In his first season in the Boston Bruins organization, Brazeau once again started in the ECHL, being assigned to the Maine Mariners to start the 2021–22 season.^[6] However, after finding success with the Mariners, he was called up to Providence after only 18 games, where he would spend the rest of the season and continue his success, scoring 15 goals for 31 points.

Brazeau looked to build off his success in the Bruins organization in 2022–23 season, and made the AHL team to start the season.^[7] Brazeau had another strong season and helped the P-Bruins win the Atlantic Division. However, the team would be eliminated by the Hartford Wolf Pack in four games in the opening round of Calder Cup playoffs.

On July 4, 2023, the Providence Bruins announced that they had resigned Brazeau to a one-year AHL contract.^[8]

In the midst of his third season with the Providence Bruins, Brazeau signed a two-year, two-way contract with the Boston Bruins on February 19, 2024. He was then called up to make his NHL debut against the Dallas Stars.^[9] Brazeau scored his first NHL goal in his NHL debut against the Stars on the same day. Brazeau's story gained attention due to his many years in the minors prior to his call-up and debut.^[10] Brazeau's size and play earned him a regular spot in the NHL lineup following his debut.^[11] He continued to prove his worth to the Bruins with his first career two-goal effort against the Ottawa Senators on March 19, 2024. Brazeau exited a game against the Nashville Predators with an upper-body injury.^[12] The injury would keep Brazeau out the rest of the regular season.^[13] He ended his rookie season with five goals and two assists in 19 games for the Bruins.