I don't get it.
To AC, my Avion itin should not be seen as an award or reward ticket. It's a fully-paid ticket to them. I get AP points on these tickets. And I gave the RBC agent my AP number so I'm pretty sure it's attached to the itin.
Don't you get to choose seats when you book fully-paid tickets on ac.com? Why should an Avion ticket be any different?