Gauthier, 18, was the Maple Leafs' first-round pick (21st overall) in the 2013 draft.
The six-foot-five, 214-pound centre has played 23 games with the Rimouski Oceanic in the QMJHL this season, posting 21 points (five goals, 16 assists) with 15 penalty minutes and a plus-5 rating.
Gauthier also represented the QMJHL against Russia in the 2013 Subway Super Series.
The native of Laval, Que., registered 60 points (22 goals, 38 assists) with 26 penalty minutes and a plus-22 rating in 62 games last season with Rimouski. His 60 points were fourth among QMJHL rookies.
Gauthier also helped Canada earn a gold medal at the 2013 Under-18 World Championship in Russia, contributing a goal and three assists in seven games.
In 85 career games with Rimouski over two seasons, Gauthier has 27 goals, 54 assists and 81 points with 41 minutes in penalties and a plus-27 rating.