Lady Gaga would likely face the same criticism for being too young for the role that Streisand received. The obvious person to cast in a film remake would be Bette Midler, of course, but I understand that she hasn't really been a box office name in some time. Perhaps you could cast someone like Tom Hanks as Horace to balance out Midler. Ironically, Streisand would probably be ideal in the role today.
I'm not sure about the idea of Streisand as a director for a remake. Sure, it would be a publicity bonanza, but her most successful films behind the camera have been smaller dramas and I'm not sure she'd have the right touch for a big boffo musical comedy, even with her experience in the genre as an actress.