Gaara solos.
Starting distance and location heavily favors him. Dealing with Kakuzu would literally be child's play for Gaara at this point. The masks are not ever getting past his ultimate defenses and taking out Gaara, especially when they can't even KO Hidan. Gaaras sand executions are way faster and much more versatile, and easily disposes of the slow masks in more ways then one. Kakuzu must camp Doton Domu to avoid being crushed at any given moment; and even then, he gets sealed away with a Sand Pyramid or buried 200m below the surface. Gaara is built for multitasking, so he could attack multiple enemies at once and defend himself all at the same time. Thus, while he's taking care of Kakuzu, and he can easily do the same with Danzo, who is a defenseless character, and heavily relies on Izanagi. Unfortunately for him, Izanagi surprise spawning gets hard countered by Gaaras automatic defense, which defends Gaara without his input. It would be no trouble at all demolishing Danzo over and over again until he runs out of Izanagi. Baku, with everything else in this match, is a lol and gets hard countered by attempting to swallow sand that Gaara controls at will.
These are two low-diff win match ups for Gaara, which may manage to make it a med-high diff win by placing them together.