as you booked with Expedia and it is cancelled way ahead of departures the OTA “own” the ticket and BA might not even have a clue how much you paid etc. It is the OTA responsibility to rebook you and it is clear by the regulation.
in some cases if the OTA book you into a public fare BA might able to take ownership over the ticket but they don’t have to.
as for EU compensation you have to submit your claim to BA as they are the operating airline in this case.
so unfortunately it is Expedia who have to come up with an arrangement.