Forrest played at the 1987 FIFA U-20 World Cup and made his debut for the Canada senior team in a May 1988 friendly match against Chile. He earned 56 caps (excluding the May 1990 North American Championship match against the US), the most of any goalkeeper in the national team's history tied with Pat Onstad and earned the most clean sheets in the country's history before retiring from international football in 2002. The highlight of his international career was undoubtedly helping Canada win the 2000 CONCACAF Gold Cup, in which Forrest was named tournament MVP and Most Valuable Goalkeeper for allowing a mere three goals and stopping two penalties in his side's five games. Also during his international career Canada had secured a 1–1 draw against Brazil only a month prior to the World Cup in the US in 1994. Forrest had further success against Brazil in 2001, recording a clean sheet in a 0–0 draw in the 2001 Confederations Cup in Japan. In 2012, Forrest was voted by the fans into the Canadian best XI in the CSA's first 100 years.