Is opera considered haram?
Like Andrea Bocelli, Pavarotti?

What if it's a female? Any difference?

If it involves songs and music which usually causes ‘tarab’ then it is prohibited to listen to it. ‘Tarab’ means the psychological interaction with the music or singing, whether it leads to joy, sadness, pride or any other emotion.
There is no difference whether the singer is male or female.
Yes. If it did not cause tarab, but the singer was female, and listening to her causes emotional effects, then it is forbidden.