Fairly simple -- Harris was the best NAT player in the West -- better than Singleton. If not for Reilly, Harris would probably have been the western nominee for MOP. Don't think we could say the same for Singleton (who did have an excellent year).
You're trying to apply an inappropriate level of logic to an argument of apples over oranges. Singleton is defense and Harris is offense. perfectly reasonable that a player can be the best D player but an offensive Canadian is the better overall player.
You may disagree, and it is very subjective when comparing O to D players, but it is not unreasonable for this to happen.
Nevermind the East/West Grey Cup, its long overdue for the CFL to get rid of the Eastern/Western nominee for the major awards. Singleton and Harris were by far the best Canadian players in the league this year, but because both are in the same division, we wont see them go head to head for the big award during Grey Cup week. A real opportunity lost as this year's award would have been talked about for a while.It might have even surpassed the MOP discussion which is always the award that gets the most attention.
Why not expand the nominations to 3, not division specific. All of the NHL individual awards are done this way. Gets 1 more player in the discussion that otherwise wouldn't have been there and ensures the best players are being talked about. With 3 players it's less likely that all would come from one area of the country.