Ruotsalainen, 23, will represent Team Finland after compiling five goals and six points in his first 17 NHL games this season. He started his first North American campaign with the Rochester Americans, scoring five goals and 13 points in 13 outings.
Before NHL and AHL seasons started, Ruotsalainen played for Ilves, scoring 16 goals in 19 games for the Liiga team.
Meanwhile, Peterka, 19, will represent Team Germany after compiling nine goals and 20 points in 30 games for Red Bull Munich, a Deutsche Eishockey Liga team. Before the DEL season started, he played with EC Red Bull Salzburg, scoring seven goals and 16 points in 12 contests for Austrian Hockey League team.
The Sabres drafted Peterka in the second round last year, 34th overall.