If they going to go star casting route, I'll say I'm Team Gaga and it's not an idea I was for even a year ago, but now...yeah I'd be for it. No Grande or Lea...I don't have any faith in Grande's acting abilities, girl needs SERIOUS training if she were at all to be considered for this, but I don't want her anywhere near it anyway. Lea...I feel like would be too obvious of a choice, plus I haven't been able to put my finger on it but there's something about her doing this role that I feel like I'd find detestable. I'm honestly not a fan anyway, never have been, so I am a bit biased...
But for reasons already mentioned here, I doubt Gaga will happen. But lets pretend for a sec. As for her acting, HER, I have faith in. Gaga has proven she's nothing if not the consumate artist who devotes herself to any project she does and lucky enough to be choosy with projects she cares about since she's, well...Gaga. She'd do the work necessary to up her acting for it. That pic is FIERCE...like, seeing that now totally makes me want her to do it, what a coup it would be and I can't imagine she won't be courted for it by the creatives, but considering her Vegas residency will run who knows how long, I doubt she'll want to be pegged as just a musical actress/singer, etc. and everything else, yeah I'm not gonna hold my breath.
Overall, I'd rather them cast the two girls with REAL chops, that goes without saying for us all, but this film will do fine, star casting or not. But we know there's alway star casting in any film, so star cast the supporting roles. Leave the leads to those with the chops and they can say the "discovered" them. If the West Side Story film can do it, so can this.