For those who has seen the original play and i heard that its a story about elderly Casanova with surrealistic opera flashbacks and ive also seen some videos about it with people singing opera (including Casanova himself).
And the all the cast are (except Malkovich) trained opera singers and not actors.
I wrote this.
Well, I have found nothing about Veronica Ferres being a trained opera singer, I strongly doubt it, she will have gotten some vocal exercise during her acting training though.
To your question whether this is a musical I must say that I don't know. I have just seen a TV news feature showing them filming some opera scenes. So there definitely will be some singing in it, but I don't know to what extent.