David Leonati, Michael MacDonald and Carlos Barahona-Villeda were part of an angry mob that attacked Robert MacKay after he tried to prevent them from breaking into the West Georgia Street store.
The attack was recorded on video and posted to YouTube.
A fourth accused, Ioannis Kangles, was acquitted, making him the first person charged with participating in the riot to be cleared.
Kangles claimed that he was trying to defend others and, at sentencing, Judge Rideout agreed, saying that it was hard to see in the video whether the defendant kicked MacKay.
The video shows MacKay being swarmed, with rioters kicking and punching him, dragging him to the ground and dousing him with pepper spray.
Police said afterwards that they had identified 15 suspects in the attack.
In May last year, two men were found guilty and sentenced to 9 ½ months for their participation in the attack.