I don't use QBO, but in the Desktop software you do the following:
Record the payment as USD253, payment in full (I assume the $20 difference is a bank charge) at the exchange rate 1.26482 (320 / 253) and deposit to your CAD bank. This will record full payment of the invoice in USD, deposit of CAD320, and the exchange loss of CAD$34. Technically the USD$20 is a bank charge (about CAD$25.30) and the actual exchange loss is $8.70, but for all practical purposes this distinction is not important and not worth the extra work to record it.
Try it.
