A native of Charlottetown, Prince Edward Island, MacEwen of Scottish descent from his great grandmother on his father's side. He was raised in Stratford, PEI while his family ran a berry farm.
MacEwen played minor midget hockey with Pownal Red Devils and signed with Moncton of the Quebec Major Junior Hockey League in 2014 after two seasons playing for Amherst, a Junior A Hockey League team in the Maritime Hockey League. He scored 40 points (10 goals, 30 assists) in 66 games of his first full season in 2015-16 and attended Anaheim Ducks training camp before being returned to the QMJHL. MacEwen was traded to Gatineau on Aug. 11, 2016.