The 22-year-old Finland international has been with Montreal on loan from Serie A side Bologna, where he signed in 2019 but never made an appearance. He appeared in 11 games for the Impact last year following his arrival, scoring five goals and recording one assist in 683 minutes.
He recorded an almost identical statline in his action in 2020, scoring four goals and dishing out one assist across 680 minutes in 13 games.
Lappalainen started his professional career with Finnish side HJK, where he scored three goals in 30 games and added two goals in UEFA Champions League and one in Finnish Cup play. He also spent two productive stints on loan in Finland with Klubi 04 and Rovaniemen Palloseura, scoring 22 goals in 60 combined appearances before signing with Bologna.