This question if list in USD or CAD pops up here often, but so far I never seen anyone mentioning this issue. In fact after so many years in business, I only learned of this now.
Americans are charged mystery banking fees if item listed in CAD
Even if PayPal does currency conversion before submitting to bank.
My friend purchased something from China seller listed in CAD using his VISA through his PayPal account and bank (M&T) charged additional $0.50. It came up as (INTERNATIONAL FEE - PAYPAL *SELLER) on the statement.
He told me he called PayPal first, they told him it's not theirs, so he called bank and they told him it was charged because "transaction was processed overseas in Toronto, Canada" 
I always use PayPal balance, but I suspect something similar may happen if Canadian VISA is used to buy from US?