Sorry, you're out of luck. You can only upgrade a flight on BA metal if it has been booked with a BA flight number. (You could
upgrade it using AAdvantage miles, if you have any or if a mechanism to transfer miles across from US is implemented in time for you. All subject to availability, of course.)
You can only upgrade with avios if it is issued by BA (e-ticket number 125-). A BA flight booked through AA with a BA flight number cannot be upgraded.