2007-08: Chosen by the Kingston Frontenacs fourth overall at the 2008 OHL Priority Selection.
2008-09: In his OHL rookie season, Gudbranson scored 3 goals and added 19 assists for 22 points in 63 games. He was a -16 for the season, and totaled 69 penalty minutes. Named captain of Team Ontario for the U-17 Championships and was a member of Team Canada for the U-18 Championships.
2009-10: In 41 games for the Frontenacs, Gudbranson scored 2 goals and added 21 assists for 23 points. He finished with a +11 rating and 68 penalty minutes in a season that was shortened due to a bout with mononucleosis. In 7 playoff games, Gudbranson scored 1 goal and added 2 assists for 3 points. Gudbranson was supposed to play in the 2010 CHL Top Prospects Game but missed it due to his illness.
2010-11: Gudbranson played well enough in Panthers’ camp to earn an NHL spot but was returned to juniors when a contract agreement could not be reached. Gudbranson played 44 games for the Kingston Frontenacs (OHL) missing time due to both team and league suspensions as well as his participation in the 2011 World Junior U-20 championship. When on the ice, Gudbranson had his best season to-date and proved to be the dominant, physical force that the Panthers envisioned when they selected him with the third overall pick in the 2010 NHL Draft. Gudbranson scored 12 goals with 22 assists and was -1 with 105 PMs. for a Frontenacs squad that was under .500 yet finished third in the East Division. In Kingston’s five-game, first-round playoff loss to Oshawa he had 1 goal (on the power play) with 3 assists and was -3 with 10 PMs. Gudbranson was one of the top players for silver medal-winning Canada at the WJC, scoring 3 goals with 2 assists and finishing +8 with 4 PMs in seven games. Gudbranson signed a three-year, entry-level deal with the Panthers in July 2011.
Gudbranson is a skilled, punishing defender who worked diligently on his offensive skills during his 2010-11 season in Kingston. He is a natural, vocal leader both on and off the ice. He has a booming shot, and has built up his offensive effectiveness through intelligent decision-making with the puck, improved up-ice passing and a better sense of when to pinch up into the offensive zone. His play in his own end is top-level, and his physical presence means that opposing forwards must always be on their toes. He is a complete defensive package, with improving offensive abilities.
Gudbranson was dealt by the Florida Panthers along with a draft pick to the Vancouver Canucks in exchange for Jared McCann and two draft picks.