On June 3, 2008, Leak signed with the Hamilton Tiger-Cats of the Canadian Football League. He was claimed by the Montreal Alouettes on June 9 after being released a day earlier. With backup quarterback Adrian McPherson injured, Leak was on the active roster for the August 21, 2009 match against the Saskatchewan Roughriders, in which he threw his first CFL touchdown pass on his first play. The Montreal Alouettes went on to win the Grey Cup in 2009.