I've yet to encounter a country where a valid, legitimately-issued credit card would be subject to the same control/declaration requirements as cash, with the card's credit limit being included in the same amount as the cash limit for declaration/control purposes. Debit/prepaid MC/V/Amex cards may be an exception and considered in some countries, but it would be rather rare at that -- as I've yet to be made aware of which, if any, countries have implemented that consideration.