Went to the CFL rule book to ensure this. In fact, the determination of offside and the line of scrimmage is altered depending on the player. For a passer, GCn20 is absolutely right, and a forward pass is legal if at least the back foot is on or behind the line. But for a snap, here is the rule:
Article 3 – Offside At The Snap
Team A players must be completely behind the line of scrimmage, except that the head, arms and hands of the Centre and Receivers may be in advance of the line of scrimmage.
By the wording of that rule (FYI “Team A” is the team in possession of the ball in all rules situations), we were offside and got away with one. Unless the offensive player is allowed to re-establish themselves onside pre-snap if no player on the other side moves, just like a defensive player can. Hard to get in the ref’s head to figure out their judgment.
One other thing I have been confused by in the past two games was why the refs sometimes blow a play dead if the defensive player jumps pre-snap and does not come in contact with the opposing lineman and tries to get back to an onside position, and other times let’s the play go. I always thought if no contact was made the play would run, and the defensive player could either re-establish themselves onside pre-snap, or the offence snaps while he’s offside and gets a “free” play. So, according to the rule, if the defensive player goes a yard or more past the line of scrimmage when encroaching the neutral zone, the play is blown dead regardless of whether or not contact is made. Also any contact and the play is blown dead immediately. So the refs can apply judgment to kill a play if they deem the offside to be beyond one yard from the line of scrimmage.