Internationally, MacKenzie represented Canada at the 2001 World Junior Ice Hockey Championships. He registered a goal and three points in seven games. He also won 58.1% of his face-offs, the eight-highest percentage in the tournament. In group play, Canada went 2–1–1 to finish third in Group B. In the playoff round, Canada defeated the United States 2–1 before losing to Finland in the semi-final. Following the loss, Canada played Sweden in the bronze medal game, winning 2–1 and earning MacKenzie his lone international medal.