Callahan, 22, made his NHL debut on March 25 against the Columbus Blue Jackets. He was second on the Grand Rapid Griffins of the American Hockey League with 26 goals and fourth with 44 points in 70 regular-season games.
Callahan was a sixth-round pick (No. 180) in the 2009 NHL Draft.
Nestrasil, 23, had 16 goals and 36 points in 70 games for the Griffins. He was a third-round pick (No. 75) in 2009.
Hopefully [Jonathan] has a year that pushes us, that is the organization, to speak to him next summer and looking for [a long-term contract]. Because the thought process is trying to get a goaltender, and hopefully it's Jonathan, to be the stabilizer for this franchise.
— Maple Leafs GM Lou Lamoriello on goaltender Jonathan Bernier