Given recent Hollywood trends, it's going to be Anya Taylor-Joy. Which while she's fairly easy on the eyes these days, I'm pretty sick of seeing her in everything.
I can't see them getting a hard trans as any major character. It's funny as an idea, but it would cost them literally 10s to 100s of millions if they did it, and they absolutely know that. It's going to be a pretty safe box-check and link is going to be a youngish actor that can be exploited for several more movies because if they just do the bare minimum, it's going to make a billion dollars.
The Switch Zelda games were gangbusters; the audience is massive and the money to be made is ridiculous. After the Mario Bros movie, they aren't going to fuck that up intentionally.