You have to enable the multi currency feature, create a new customer profile with the USD currency, set a USD bank account, then you may create the invoice.
Other options to seek a lower fee and a better exchange rate:
1. Utilize this payment service
2. Open a multi currency virtual bank account at TW and utilize the bank feeds.
It's awesome that you have customers beyond the border. I hope it means your business is doing well, and I know how important it is to be able to account for foreign currency transactions in your books. You've already got a bit of information to start with the other response on this thread and I'd be happy to flesh out the options so you know what you can do with QuickBooks Online.
QuickBooks Online makes it easy to record foreign currency transactions once you've got the multicurrency feature turned on. This feature is available in Essentials and Plus packages of the program at no extra cost, and it gives you the option to set up customers, vendors, and even accounts in your Chart of Accounts with a foreign currency. This article is a good place to start to learn more: About Multicurrency
It sounds like you may also be interested or are already using QuickBooks Payments, which is an add-on service that allows your customers to pay their invoices online with a credit card. At this time, this feature can only be used for Canadian currency transactions. This article has more details about that: QuickBooks Online Payments overview
Since QuickBooks Payments cannot process foreign currency transactions, including USD, considering a third-party option is the way to go. I see Fiat Lux has recommended a payment service, and you can also research the options available to connect with QuickBooks Online by using the Apps tab in your account to find the best fit for you. These won't operate exactly the same as QuickBooks Payments, meaning you wouldn't see an embedded link on the invoices themselves, but there are still options to easily accept payments from customers.
I invite you to leave feedback about the options available for accepting virtual payments through QuickBooks Payments. In the How do I submit feedback? article, you can learn the steps to take to share your thoughts with us about how we can further grow the program. Our goal is to offer business owners and bookkeepers the features they need to manage their books, and feedback helps us do that.
I'll be around if you have more questions, so don't hesitate to ask. I'm here to help!