Gaara wins.
- Pretty sure that there was a forest near Great Naruto Bridge, so Gaara can just fly over there and make extra sand. He can fly out of Baku's suction range, protect himself with a shield of sand, and give Baku a tasty sand dinner and overwhelm it.
- Shield of sand + Third Eye allows Gaara to tank Danzō's attacks and observe his first respawns, then he can spread his sensor sand all around the area and around his perimiter. Juinjutsu isn't working here when Gaara's sand defense is automatic and even blocked Amaterasu.
Edit: I was still referring to the bridge where Danzō and Sasuke fought. I just mixed up the name. Samurai bridge instead of GNB