For tax return purpose, you should use the exchange rate of the Bank of Canada, not the rates by other exchange institutions (CRA will correct you with the Bank of Canada rate). You have two options: annual rate or individual date rates. if your income was paid on many dates in the year, to save time,you had better use the annual rate to calculate. However, you always can use the rates on the dates when you got your payments. you calculate each at the individual rate and sum the result. You may want to try both of them and see which option is better for you to save tax. either way is acceptable by CRA. Good luck!