Allen first played U Sports football for the Guelph Gryphons for four years, recording 63.5 tackles, 5.5 sacks, one forced fumble and three fumble recoveries.[3][4] He was then selected by the Saskatchewan Roughriders of the Canadian Football League (CFL) in the fourth round, with the 35th overall pick, of the 2020 CFL draft. However, the 2020 CFL season was later cancelled due to the COVID-19 pandemic. He officially signed with the Roughriders on January 19, 2021.[5][6] Allen did not make the team and was sent back to Guelph for another season.[3] In his fifth and final season at Guelph in 2021, Allen totaled 58 tackles, three sacks and two forced fumbles in seven games, earning All-Canadian and Ontario University Athletics (OUA) All-Star honors. He was also named the OUA's most outstanding stand-up defensive player.[3]
Allen re-signed with the Roughriders on December 14, 2021.[7] He was placed on injured reserve on June 17, 2022, and activated from injured reserve on July 28. He dressed in 12 games during the 2012 season, recording six defensive tackles and six special teams tackles.[8][2] Allen dressed in all 18 games in 2023, accumulating 19 defensive tackles, 19 special teams tackles, and one pass breakup.[2]