It can go either way but I lean more towards Gaara, especially since he has Shukaku and can fly, not to mention his defense pretty much cancels out almost all of Pain's attacks.
Most of those paths are useless against Gaara's defense. The summons are useless. They get crushed with simple Sand Tsunami or Sand Waves.
The only reason why Gaara lost to Deidara was because he was protecting his village and trying to fight Deidara at the same time. In this case, Gaara will only be occupied on killing Pain, so there will be no BS tactics.
Gaara can fly so small melee attacks are useless, not to mention he can attack from underground and grab their legs and crush them beneath the earth. The pains have no speed feats so they will not out-speed Gaara's sand once their legs are caught and they can't move.
The only way that Pain can win is if he uses CT, as I see no way for Gaara to escape that, but once he uses that he will be completely drained and will have to wait before his chakra can recharge.