Welcome to FT!
Assuming the itinerary OP is looking at has at least on leg of flight operated by AC, then there would be a difference between ANA inventory (partner) and aéroplan inventory (self).
When you see an AC flight on ANA website, then it's partner, and then it is rather common that there is only one seat available. Your account is irrelevant and it would not make a difference even if you call.