Anakin wanted a girl, not a boy. Rather, he knew it was a girl, not a boy. Knew the girl would've been powerful. Knew he'd've doted on her, like the princess she would have been.
Vader doesn't care. His child is powerful, that's all that matters. The boy will destroy the Emperor, and together they will rule the galaxy, making things right—
(but he's too much like his mother, and he won't give up and he won't fight and he keeps speaking platitudes and he won't use his emotions like she might have—)
but Vader and Anakin both love Luke. Because he's his mother in all save looks.