Dellandrea, 18, spent the 2017-18 season with the Flint Firebirds of the Ontario Hockey League (OHL), posting 59 points (27-32=59) in 67 regular-season contests. The Toronto, Ontario native led the team in goals (27) and ranked second in points (59) and assists (32). In two seasons with the Firebirds, he amassed 83 points (40-43=83) in 124 regular-season contests. Dellandrea skated in five games during the 2017 OHL Playoffs and recorded one assist (0-1=1).