Kapanen, 22, was due to become a restricted free agent this summer after coming off an entry-level contract. He scored 20 goals and 24 assists in 78 games last season for the Maple Leafs, who were eliminated in the first round of the Stanley Cup Playoffs by the Boston Bruins.
In seven games during the post-season, Kapanen had one goal and one assist.
Toronto still has pending-restricted-free-agents Mitch Marner and Andreas Johnsson left to sign.
More to come.