Akinola leads all players in the tournament with five goals.
The teams combined for five goals in the opening half of the wild game played without fans at ESPN's Wide World of Sports Complex. Saphir Taider converted two penalty kicks for the Impact.
Richie Laryea gave Toronto the early lead with a hard shot to the far post as Montreal's defending sputtered. Laryea, a defender, was playing for Justin Morrow, who was held out of the game with Achilles tendinitis.
Taider converted his first penalty to pull the Impact into a 2-2 tie, but moments later Akinola scored his second goal to put the Reds back in front.
Akinola's third goal came in the 83rd minute. Clement Diop rushed toward him but Akinola jumped to avoid the goalkeeper and score. It was the first hat trick in the series between the two teams.
Taider got his second PK in stoppage time for the final margin.
Akinola, a Homegrown Player in his third year, scored twice in Toronto's tournament opener, a 2-2 draw with D.C. United.
The Reds were without forward Jozy Altidore for the second straight game. Altidore had just returned to full team training on July 3 after a 14-day quarantine in Canada. He trained in the United States during the league shutdown.
Toronto's Jonathan Osorio also was held out as he recovers from a quad injury.
The Impact opened MLS is Back with a 1-0 loss to New England.
Montreal is playing its first season under coach Thierry Henry, the former Arsenal striker who also played in MLS for the Red Bulls. The Impact won the opening game of the season 2-1 against the Revolution. They played to a 2-2 draw with FC Dallas before the season was shut down because of the coronavirus.
Toronto, which won the MLS Cup title in 2017, played to a 2-2 draw against San Jose in the regular-season opener before a 1-0 victory over NYCFC.