Kakashi would win. Even if Gaara got him with sand prison Kakashi would get out with his many jutsu. Actually it depends where they battle... if dessert Gaara would win... if anywhere without sand Kakashi would win. MS used on Gaara's gourd. Gaara wouldn't be able to do anything. So i would say Kakashi. But also why would they battle in the first place?
Gaara would completely destroy Kakashi. Kakashi could not defeat Deidara until he used Sharingan. You'd say Gaara lost to Deidara too but he lost because he was* trying to protect his village.
Ah, but that's where you're wrong, Kakashi didn't need to use MS to defeat Diedera.* Remember that he wanted to end it quickly and not draw it out.* I'm sure he could have easily killed Diedera as easily as he could beat Gaara.