This is kind of funny. When I watched the movie Avatar way back in 2009, I was struck by the similarity of the premise to Timothy Zahn’s 2002 novel Manta’s Gift:

The main character, a human who’s suffered a severely disabling injury, is offered the chance to place his consciousness into an alien body and report back to the human expedition. Over the course of his time there, he finds that he has more in common with the aliens than with the humans who sent him, and pushes back against their exploitative agenda.

OK, so it’s a brain transplant, not a neural link, and it’s manta-like beings who live in the groundless atmosphere of Jupiter, not humanoids who are part of a literal Gaia.

I just discovered that the book was re-issued in 2020 (Timothy Zahn, 2002) with a tagline describing it as “A gripping first-contact adventure for fans of James Cameron’s Avatar…”