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You may explore this service to deal with multi-currency transaction. It supports QBO
But if you have a subscription business, you may consider using a recurring billing app and sync it with your QBO.
Hope it helps.
You can subscribe to QuickBooks Payments, so your Canadian customers can pay you via credit cards, or bank transfers.
Their credit card needs to have a 5 digit zip code compatible with the US standards. If this isn't the case, they can contact their credit card-issuing bank and ask for options regarding this matter.
Another option for you is to search for a 3rd party app in the QuickBooks App Store that meets your needs.
Take a look at this article to learn more about how you can process credit card payments: Process a credit card payment in QuickBooks Online.
Let me know if you have other questions by dropping a comment below. I'll get back to you as soon as I can.