Koppanen completed his second season with the Ilves Under-20 Team of the Junior A SM-liiga (top Finnish junior league) in 2016-17, posting 23 goals and 31 assists for 54 points with 18 penalty minutes and a plus-28 rating in 38 games. The 6-foot-5, 194-pound forward also skated in six playoff games, tallying two goals and four assists for six points with a plus-three rating. Koppanen appeared in 40 games in his first season with the Ilves Under-20 Team in 2015-16, compiling nine goals and 17 assists for 26 points with 14 penalty minutes and a plus-12 rating.

Koppanen has represented Finland in international play on several occasions, most recently skating in 10 games with the Finnish Under-20 Team in 2016-17, notching three goals and three assists for six points with a plus-three rating. The 19-year-old forward also won gold with Finland at the 2016 World Junior Championships. In 40 career games of international play, Koppanen has recorded five goals and six assists for 11 points with 12 penalty minutes and a plus-four rating.

The Tampere, Finland native was selected by the Bruins in the fifth round (135th overall) of the 2016 NHL Entry Draft.