After the Quebec Junior A League shut down, Perreault joined the Montreal Junior Canadiens of the Ontario Hockey Association (OHA) for the 1967–68 season, the first of three years with the Junior Canadiens. His 49 points in 47 games helped the Junior Canadiens to a second-place finish. During his second year on the team, one that included future NHL talents Réjean Houle and André Dupont as well as future professional teammates Jocelyn Guevremont and Richard Martin, Perreault blossomed. His 97 points were second on the team to Houle's 108 points, and they earned him OHA First All-Star Team honours. As Perreault blossomed, the team excelled. In his second season, the team finished first in the OHA and won the 1969 Memorial Cup Canadian Junior championship. It was the first Memorial Cup win for Montreal since 1950.