Credit card companies' rules state that only Visa Credit and MasterCard credit can be charged in USD for a company based in Canada.
All other cards, Amex, discover, Visa Debit, Mastercard Debit, prepaid card, Diners Club, etc... can only be charged in Canadian currency.
If you don't want to be charged in CAD and avoid the exchange fees, then use a Visa Credit or Mastercard Credit. With those cards the charge will be in USD exactly as shown in the list.
We don't set the rules, we have to abide by them.