Kakuzu wins this, it might cost him a heart of two, but he will win it.
honestly I don't see Sasori winning this fight, not even by a long shot.
Sasori relies on puppets and his poison to win matches and we have seen that the individual puppet aren't really that strong, it's their shear numbers and the fact that their weapons are coated with poison that wins Sasori his matches.
However poison won't work on Kakuzu, sure if a poisoned blade or weapon would pierce true Kakuzu (or one of the thread monsters, if Kakuzu decides to release them) and hit the heart then the poison would take affect, but unless the heart is physically injured by a poisoned weapon then it won't have an affect on Kakuzu sins his, well everything under his skin have been replaced with the black threads. (there are no blood vessels to spread the poison... everything except the hearts have been replaced by the forbidden technique Kakuzu stole)
and even if Sasori manages to destroy one of the hearts that way there are still 4 more to go, and I'm not even taking Kakuzu main line of defense and attack in to the arena here, his Doton Domu, if he uses that no blade will be able to even penetrate his skin, then what?
Sasori would be forced to use his strongest puppet very early on in match do to the fact that none of his regular puppets can do much more than slightly annoy Kakuzu for more than a few minutes. (and this is me being polite here, if he would start spamming a barrage of elemental attacks he would do it a lot faster)
My point is this: If early time skip Sakura are able to react and reflect the iron sand then so are Kakuzu with Doton Domu.
This is simply a very bad match up for Sasori, in fact it's literately the worst Akatski match up he could possibly have... Now does this mean that Sasori would be killed in this fight? properly not, it's very likely that he would either manage to get away or hide his real body, or put his heart container in another puppet and survive the match that way, I would say that it's very likely that Sasori would survive this match, however he would not win, in fact he would not even come close to winning the match, he will be defeated if he was matched against Kakuzu.
