Good news for me trying to resell. I would hazzard to guess now that VW/Audi Canada are now operating as separate entities from VWoA they will be more competitive to defend the border.
Really, these letters advising not to sell are just that. You can likely find a dealer that will want to make the sale bad enough. OR you can find a dealer with a demo/lightly used with some kms (I think it's 7,000 or 11,000kms) where the rules don't apply.
The dealer runs the risk of getting caught, at which point they run the risk of their wrists being slapped (fine/reimbursement of difference between US and Cdn price/restriction of units shipped to the dealer). Where risks are involved, some will take them.
So long as US VIN vehicles are okay for warranty work at Cdn dealers, I'd try calling around. You may get the standard response initially - after all, they want to be sure you're ligit and not VWoA testing them or something, but I would bet you could find yourself something.