Nelson made his debut for the Canada national under-17 team in the 2019 CONCACAF Under-17 Championship on May 2, 2019 against the United States. Against Guatemala in the second game of the group stage, Nelson scored a hat-trick in a 4–2 win. Nelson scored twice more in the tournament – against Curaçao and Costa Rica respectively – as Canada qualified for the FIFA Under-17 World Cup for the first time since 2013. At the end of 2019, Nelson was named the Canadian Men's Youth International Player of the Year.