If you have already submitted your application, you can always join an explanation letter/webform. You can mention in that letter that per x date, the currency exchange of USD to CAD was XYZ. you can look it up here in this website of bank of canada : https://www.bankofcanada.ca/rates/exchange/daily-exchange-rates-lookup/
Mention that this is the exchange rate as per the Bank of Canada. You can also mention that you are able to cover the discrepancies if needed per IRCC request.
Mention that this is the exchange rate as per the Bank of Canada. You can also mention that you are able to cover the discrepancies if needed per IRCC request.