Did you buy something in US$ with your credit card, but your credit card only reports the total in Canadian Dollars, so you don't know what they charged you, or what their commission was?

Here is the daily US Dollar to Canadian Dollar Exchange Rates, noon-time rates. Data is from business days only. Generally, changes are minor on holidays and weekends (though it is true that the forex market is open 24/7 and rates are constantly fluctuating).