On June 28, 2013, Gauthier was invited to the Canadian National Junior Team summer development camp. After making the roster, he was a member of the gold medal-winning Canadian team at the 2013 IIHF World U18 Championships. The following year, he was again invited to the Canadian National Junior Team summer development camp prior to the 2014 World Junior Ice Hockey Championships. After making the final roster, Team Canada lost in the semi-finals to Finland and failed to medal against Russia. While playing in six games, Gauthier recorded one assist and ended with a -2 Plus–minus.