Burnham was signed as a free agent by BC Lions in May 2014 for the upcoming season. Initially playing on the practice squad, he made his pro debut in Week 13 against the Toronto Argonauts, in which he caught five passes for 90 yards and a touchdown. His season was cut short one week later when he suffered a lacerated spleen.Click highlights and college tabs at In his second season in the CFL Burnham played in 11 games catching 35 passes 423 yards with 2 touchdowns. Burnham had a breakout season in 2016, playing in all 18 games for the first time in his career he set personal bests in catches, yards and touchdowns. His 1,392 receiving yards was fourth highest in the league that year. Burnham was set to become a free agent in February 2017. On December 6, 2016, Burnham had a workout with the Minnesota Vikings, and a workout with the New York Jets on December 15, 2016. According to BC Lions head coach Wally Buono, Burnham had workouts with somewhere between 10 and 12 NFL teams between the end of the 2016 season and January 31, 2017, at which time pending CFL free agents were no longer allowed to work out with NFL teams until their contracts expired on February 14, 2017. On February 10, 2017, Burnham and the Lions agreed to a two-year contract extension. Over the following two seasons Burnham continued to be a key part of the Lions passing attack, catching over 148 passes for 2,231 yards with 16 touchdowns. Identically to two years prior, on February 10, 2019, Burnham and the Lions agreed to a two-year contract extension. He had a career-high 100 receptions for 1,492 receiving yards and 11 touchdowns en route to being named a CFL All-Star. Following the cancellation of the 2020 season Burnham and the Lions agreed to a new contract extension on February 1, 2021. Burnham was once again named a CFL All-Star following the 2021 season, posting 67 receptions for 965 yards and five touchdowns. Burnham suffered a punctured lung and broken ribs on June 25, 2022, and it was announced he would miss the next 3-6 games. Later in the 2022 season he suffered a fractured wrist. He was placed on the six-game injured reserve list on September 26, 2022. Burnham ended up missing half the season with injuries and caught only 41 passes, his lowest total since his second season in the league (2015) in which he caught 35 passes.
