It's a hard fought battle but I believe it can go either way depending on the length of the battle. We've seen tremendous feats from both Tsunade and Kakashi in this war, Tsunade has proven she can do more than bark orders, in fact the reason the kage even lasted as long as they did against Edo Madara was because of Tsunade.
The same can be said for Kakashi, he is the reason Naruto, Gai, and Bee have been able to keep up with Obito for this long. his intelligence and strategical prowess put him in the same league as ninja like Naruto, Sasuke, and Itachi. Strength alone doesn't win fights as Kakashi demonstrates this well in almost all of his fights.
In my opinion the longer the fight goes on the better it will be for Tsunade, being a Senju her massive amount of life force and chakra make her extremely durable. Kakashi's ace in the hole is Kamui, he only needs to warp away an arm or leg to completely cripple Tsunade and from there win the fight. We've seen Tsunade's speed in the battle against Madara, so we know she's more than capable of dodging Kamui.
Tsunade's massive strength basically means its a one hit KO if she manages to hit Kakashi, there in itself is a problem for her though. When we look back at all of Kakashi's fights we see that he uses clones to scout out his opponents fighting style and Jutsu. We've also seen from his battle with Kakuzu and Hidan that he is quite nimble and very aware of his surroundings. He managed to sucessfully dodge several elemental attacks, as well as Hidans physical attacks, while at the same time going toe to toe against Kakuzu and his impressive taijutsu.
In conclusion it comes down to the length of the battle. If Tsunade can dodge all of Kakashi's attacks including his Kamui and draw out the fight she can win, otherwise I say Kakahi wins.
