The Avion / CWT call centre will gladly do seat selection for you..... I don't believe you can preselection seats via aircanada.com for a GDS booking
Can you explain why the Avion agent couldn't do the seat selection over the phone when I booked the itin a couple weeks ago?
By the way, at the time I booked the itin, I asked the RBC rewards agent if or when they'd have an on-line portal to book these reward tickets, and I was told they had it already - it apparently went live on Dec 1.