Bad Luck Fale
Zack Sabre, Jr.
The promotion didn't reveal which of the two blocks each wrestler will be in, but at least we know all the entrants.
The G1 Climax is a round-robin tournament that runs from July into August. The wrestler at the top of Block A will wrestle the winner of Block B on the final show. The overall G1 Climax victor will then challenge whoever is IWGP Heavyweight Champion at the Tokyo Dome on January 4th 2018 (unless they win the title shot in matches leading up to the Dome show).
I said it last year, but was wrong. I'll write again simply because it makes the most sense to me - Naito is my pick to win.