Tambellini competed for the Canadian national junior team at the 2004 World Junior Championships, held in Finland. He was the lone NCAA player on Canada's roster. Playing against Ukraine in the round-robin, he scored his first international goal in a 10–0 win. Helping Canada reach the gold medal game, they lost to the United States by a 4–3 score, earning silver. In six games, Tambellini recorded two goals and five points, ranking sixth in team scoring.