2010-11: Alex Coulombe played 22 games for the Magog Cantonniers in Quebec Midget AAA hockey (including 12 playoff games); spending most of the season with the Marie-Rivier Canimex Midget Espoir in suburban Montreal. He had no points with 4 penalty minutes skating for the Cantonniers. Coulombe scored 3 goals with 4 assists and had 58 penalty minutes in 30 games with Marie-Rivier. He was selected by Valleyfield in the 14th round (191st overall) of the Quebec Junior AAA Draft.
2011-12: Coulombe played in 43 games for Magog in his first full midget AAA season. He scored 5 goals with 9 assists and had 36 penalty minutes. The Cantonniers finished fourth in the Reebok Division. Coulombe had 1 assist and 4 penalty minutes in four playoff games.
2012-13: Coulombe attended Stanstead College prep school in Quebec and skated for the school's hockey team. In 55 games (including tournament play) he scored 7 goals with 24 assists and was +5 with 129 penalty minutes. He committed to playing college hockey at the University of Vermont in 2014-15 and was selected by Soux Falls in the 12th round (179th overall) of the 2013 USHL Entry Draft. Coulombe, ranked 91st amongst North American skaters in Central Scouting's mid-term rankings, was ranked 68th in the final rankings prior to the 2013 NHL Draft.