Miller has represented Canada in several international competitions. In July 2017, he competed for the Canada team that won a gold medal at the FIBA U19 World Cup. Miller averaged 1.6 points and 1.7 rebounds per game. In June 2018, he was a key piece for the Canada team that captured a silver medal at the FIBA U18 Americas Championship. Miller averaged 17.3 points, 7.3 rebounds, 1.5 assists and 1.2 steals per game. In the semifinal win against Puerto Rico, he posted 31 points and 14 rebounds.