Hamhuis played for the Canadian national junior team at the 2001 and 2002 World Junior Championships. He won a bronze medal with Canada in his first year at the tournament in Moscow, Russia, contributing an assist in seven games. The following year in Pardubice, Czech Republic, he recorded three points in six games, tying with for Carlo Colaiacovo for the team lead in scoring among defencemen. He was sidelined during the tournament with an injured shoulder, sustained after being hit from behind into the boards in a game against Russia. He returned to help Canada to a silver medal, losing in the gold medal game to Russia 5–4.