When paying to businesses with Settle, the business decides what currency they accept, but you can charge any of your cards or accounts, and you can choose to spend with whatever currency you like.
Settle will automatically do the exchange calculation and serve you a valid rate for a period of time. You will see the total amount you will be charged for the transaction, including the exchange rate and possibly cross-border fees, as you send to the business the amount they have requested in their decided currency.
Find detailed instructions on how to Pay to a business here.