I'm no expert on the matter, but it seems wanting to have a Western Sydney team is driven more by desperation than by public demand. The FFA seem worried that they are getting swamped by the other 'football' codes in the region, but if that is the prime motivation then they may have left it too late. If the Canberra bid has a much higher public demand factor, then imo it's a much better option.
The worst thing for the A League would be for the FFA to repeatedly make poor decisions as to where to put a team, only for that team to collapse in a year or two, over and over again. Public support is key to avoiding that.
What they need to do is build a better league, THEN try it. Instead of trying to force it, failing, and making it even more impossible for themselves.
Canberra would go a long way to help them do that by the sounds of it.
Expansion needs that organic aspect, you cannot just throw a franchise into a community and expect them to follow it.
West Sydney has the player base, but doesn't seem to have the drive to get their own team. The FFA want a team there for the added value it would give the TV rights by having a Sydney derby.
Canberra has a bid set up, local support but just missing a dodgy Greek needing a haircut.