I think Gaara and Guy would win this one. Guy and Kakashi still seem pretty even to me, if Kakashi's not only slightly stronger: However, with the type of Jutsu Gaara has, Hidan wouldn't stand a chance against him. Gaara and Guy united should be enough to turn the tables against Kakashi.
gaara would have a huge advantage over hidan's close range combat. he wont get anywhere near gaara. he'll get sabuka sabusu or sabuka ryusa instantly.
gai and kakashi is pretty even. who ever wins this win the fight.
if gai wins, it'll be by going 7 or 8 gates.
if kakashi wins, it'll be a close one and in a act of pure genious. than he'll make quick work of gaara. hes raikiri will break through all of gaara;s sand.
but i say gai wins this. i dont see anyone beating gai when he goes 8 gates
Depends whether or not Gaara is able to stay far, far away from Kakashi's Raikiri. The sand is strong, but not impervious. And unless Gai opens some gates, fast...without prior knowledge, Hidan destroys him.