CFL now allows teams to replace any Canadian starter who suffers an in-game injury with a veteran American, defined in the new agreement as a player with at least four years in the CFL or three with his current team.
A "true" National could also replace him.
Another stipulation is that the same ratio split (the number of Canadians on offense and defense) must be retained throughout the game. Teams for instance cannot replace an injured Canadian wide receiver with a veteran American defensive lineman.
There is concern that teams could benefit if a Canadian is injured. A Canadian could be hurt for as few as 1 play for the rule to come in effect. So essentially, teams are on the honor system to make sure they comply with the spirit of the rule change.
Roster sizes are limited so potential abuse should be limited. For instance, a Canadian offensive tackle could not fake an injury and be replaced by an American offensive lineman because teams do not dress backup American OL.
Question is: will this replacement rule be a disaster and be done with a new CBA is negotiated one year from now, or will it be just a non-factor?
I would guess people will only notice if the player change is made right before a significant play that determines the outcome of the game.