2009-10: Lagace played midget AAA hockey in Quebec with the Seminaire St-Francois Blizzard. Playing for the top team in the Quebec league, he split the goaltending duties with Sebastien Auger and in 22 games was 18-3 with a 1.86 goals against and .930 save percentage. In two playoff games he was 1-1 with a 3.55 goals against and .857 save percentage. Lagace was drafted by Prince Edward Island in the second round (20th overall) of the 2010 QMJHL Entry Draft.
2010-11: Lagace played in 18 games for the PEI Rocket as a backup to QMJHL veteran Evan Moshner in his first season of major junior hockey. He was 8-4 with 1 shutout and had a 3.59 goals against and .884 save percentage. The Rocket made the playoffs after finishing fourth in the Maritimes Division. Mosher started all five games in the playoffs.
2011-12: Lagace took over as the starter for the PEI Rocket in his second season; playing in 56 games. The Rocket had the QMJHL's worst record, winning just 19 games, and Lagace was 12-39 with 5 overtime losses and 1 shutout – finishing with a 4.51 goals against and .867 save percentage. Lagace attended Dallas' prospect camp and was signed to a three-year entry-level contract in July 2012.
Butterfly goalie with decent size and reflexes. Has a strong glove hand and uses his stick well along the ice. Still needs to improve and refine his movement in the crease. Has good pads and can stop a lot of shots down-low. Fairly compact and can be prone to allowing high shots. Rebound control is a concern as it is with most young goalies. Has had to withstand a copious amount of quality chances playing for Prince Edward Island (QMJHL) and hopefully he can keep a cool demeanor and learns quickly not to get down on himself for giving up goals.
Will return to the PEI Rocket (QMJHL) in 2012-13.