2009-10: Brandon Montour skated for the Cambridge Hawks minor midget AAA team in Ontario. He scored 4 goals with 14 assists and 12 penalty minutes in 40 regular season games and had 2 assists and 6 penalty minutes in 11 playoff games.
2010-11: Montour played for the Brantford Golden Eagles in the Greater Ontario Junior Hockey League as a 16-year-old and played for the Cambridge Hawks midget AAA team. He scored 1 goal with 13 assists and 22 penalty minutes in 37 regular season games for Brantford and had 3 assists with 6 penalty minutes in 10 GOJHL playoff games. Montour scored 3 goals with 8 assists and 38 penalty minutes in 19 midget games with the Hawks.
2011-12: Montour returned to Brantford for a second season as the Golden Eagles finished first in the GOJHL's Mid-Western Conference and won the playoff title; falling to Golden Horseshoe Division champion St. Catharines in the Sutherland Cup final. Montour scored 14 goals with 22 assists and 65 penalty minutes in 51 regular season games and scored 6 goals with 12 assists and 30 penalty minutes in 19 playoff games.
2012-13: Montour went from Brantford to the Caledonia Corvairs in his third GOJHL season. In 49 regular season games he scored 18 goals with 49 assists and 94 penalty minutes. Caledonia finished first in the Midwestern Conference but lost to Montour's former team, Stratford, in the playoff semifinals. In 12 playoff games he scored 4 goals with 11 assists and 22 penalty minutes. Montour was selected by Waterloo in the 18th round (267th overall) of the 2013 USHL Entry Draft.
2013-14: Montour was named the USHL's top defenseman and was the second-leading scorer for Western Conference champion Waterloo as a 19-year-old. He committed to playing college hockey at Massachusetts-Amherst in 2014-15 in September before scoring 14 goals with 48 assists and finishing +35 with 36 penalty minutes in 60 regular season games. After finishing first in the regular season the Black Hawks advanced to the Clark Cup finals against Eastern Conference champion Indiana. Montour was ranked 92nd amongst North American skaters in Central Scouting's final rankings prior to the 2014 NHL Draft.