2009-10: Cairns played for the Hamilton Junior Bulldogs Midget AAA team. In 61 games he scored 21 goals with 33 assists and 44 penalty minutes. He was selected by Erie in the third round (50th overall) of the 2010 OHL Priority Draft.
2010-11: Cairns skated in 60 games for Erie in his first OHL season. He scored 6 goals with 12 assists and was minus-15 with 8 penalty minutes. After winning 40 games during the regular season, the Otters lost to Windsor in a tight seven-game series. In six playoff games Cairns had 1 assist and was -2 with 2 penalty minutes.
2011-12: Cairns skated in 63 of 68 games for Erie in his second season. The Otters finished with the league's worst record, winning just ten games. Cairns finished as the team's fifth-leading scorer, with 13 goals and 20 assists and had 28 penalty minutes. He scored 4 of his 13 goals on the power play and was minus-57 on an Otters team that gave up twice as many goals as it scored (338-to-169). He was ranked 189th amongst North American skaters in Central Scouting's final rankings prior to the 2012 NHL Draft.
Cairns is a player that competes hard but has offensive abilities that aren't well developed as yet. His primary role is as a two-way player who will bring a good effort game-in and game-out but is not highly skilled. His future should he make it to the NHL is as a third- or fourth-line player.