How liable is VW? Well returning a car you have driven for several years just is not the law in Canada. There has been a value to the vehicle even if it is not what it was represented to be.
So assuming there was a representation that was intentionally false - a fraud - and that's a big IF the real question is damages.
And here too there is an issue.
What did VW owners actually lose? Perhaps they thought they were getting a Green Car and in fact it was a stinky old diesel but even if that is true what financial harm did they suffer? Likely none.
So damages would be notional at best.
All that said, regulatory action may be severe and VW isn't out of the woods but i don't see a significant consumer claim approaching.