During his third OHL season, Horvat was named to Canada's under-20 team for the 2014 World Junior Championships in Malmö, Sweden. After beginning the tournament in an offensive role, centring a line with Connor McDavid and Sam Reinhart, he finished on Canada's checking line and earned praise from head coach Brent Sutter for his defensive play. In seven games, he recorded a goal and three points as Canada ranked fourth.