Kapanen, 19, appeared in four games with the Leafs after being recalled from the Marlies on Feb. 29. Kapanen has eight goals and 14 assists in 32 games with the AHL squad this year.
Leipsic, 21, had a goal and two assists in six games with the Leafs this year. He has 16 goals and 21 assists in 50 games with the Marlies.
Leipsic was a 2012 third-round pick of the Nashville Predators before being dealt to Toronto on Feb. 15, 2015.