2008-09: Johan Sundstrom split the season between Frolunda's two U-18 teams as well as competing for Goteborg in the Swedish TV-Pucken tournament for high-school-age players. With the top team in the Elitserien U-18 league, Sundstrom scored 2 goals with 2 assists and had 2 PMs. Competing at the Allsvenskan (second) level, he scored 4 goals with 5 assists in 12 games and added two assists in seven playoff games. In eight games for Goteborg, he had 3 goals and 8 assists. Sundstrom also played in three international contests for Sweden at the U-17 level, garnering one assist.
2009-10: Sundstrom made his Swedish Elite League debut, appearing in one game for Frolunda but it was his play with the U-20 team that was most impressive. In 38 games including one playoff contest, he scored 17 goals with 30 assists and had 14 PMs. Sundstrom also played in 5 games with Frolunda’s U-18 team scoring 6 goals with 4 assists. While he did not compete at the World Junior U-18 championships, he appeared in 14 international contests with Sweden's U-18 team and had 5 goals with 10 PMs.
2010-11: Sundstrom appeared in 41 games for Frolunda in the Swedish Elite League. In limited ice time with the Indians, who finished in 9th place in the twelve team league, he scored 1 goal and was -7 with 10 PMs. Playing for Frolunda's U-20 team Sundstrom was a dominant force. In 22 games, including playoffs, he scored 18 goals with 16 assists and had 6 PMs. Sundstrom was named to Team Sweden for the World Junior U-20 championships and had one assist in six games for the fourth-place squad. Sundstrom was ranked 24th among European skaters in Central Scouting's final rankings and was selected by the Islanders in the 2nd round (50th overall) of the 2011 NHL Draft.
2011-12: Sundstrom skated in 49 games in his second season with Frolunda in the Elitserien and won a gold medal with Sweden's U20 team at the 2012 World Junior Championship. He scored 6 goals with 5 assists and was plus-six with 8 penalty minutes during the regular season. Frolunda reached the playoff quarterfinals after finishing in fifth place. Sundstrom was minus-two with no points in limited ice time in six playoff games. In six games at the WJC he scored 1 goal with 4 assists and was plus-five with 2 penalty minutes. Sundstrom signed a three-year entry-level contract with the Islanders in June 2012.
Sundstrom has the bulk and strength of a power forward and has the requisite skills to play in small, tight areas. He plays a disciplined, two-way game and is effective at both ends of the ice and in all situations. He is not a dazzling or flashy offensive player but skates well and put up big scoring numbers playing at the junior level in Sweden.
Sundstrom has moved to North America to play for the AHL's Bridgeport Sound Tigers in 2012-13.