Round 1: FRS Naruto, Hebi Sasuke and early shipuuden Sakura
Naruto was stated to be about equal with Kakashi, and Sasuke was stated to be weaker than Armless Orochimaru. Sakura isn't doing anything.
Round 2: Sasori and Deidara
With Tsunade's regeneration and Raiton, Tsunade may be a great counter against Deidara. Sure, she lacks range, but she can throw things. Jiraiya could support her too. Orochimaru may also be a better counter against Sasori, since sharp things and poison won't have too much effect on him and he can counter the 100 puppets with giant snakes to smash them like little G.I.Joes. Jiraiya could help either of them to increase their chances of victory.
Round 3: Hiruzen, Danzo and Chyio (Hiruzen has e do feats and KA is restricted)
This would be a fairly interesting battle. I'm confident that the Sannin take it, Orochimaru especially would be privy to Izanagi.
Round 4: Six Paths of Pain
Jiraiya could had won alone, with the other two it's overkill.
Round 5: Itachi (healthy) and Kisame
Alright, then I'm going to mod the Sannin too. But no, Jiraiya is at least equals with Itachi and Orochimaru could beat Kisame. Orochimaru too could give Itachi trouble while Jiraiya beats Kisame. With Tsunade there as support and to play the numbers game, the Sannin win.
Question: Would Orochimaru get Itachi's body for the next 3 rounds?
Round 6: Current gokage (minus Tsunade)
3 against 4 This is a tough one too. If Orochimaru has a good shot of beating Ei since he can't make Orochimaru stay down; Orochimaru's poison and Kusanagi will likely do the trick for him. Jiraiya can tackle Gaara, his oil and huge summons will be a bane for Gaara. But then that leaves Tsunade with Onoki and Mei. I can see Mei as the weakest link and Tsunade may be lucky enough to take her out first, evening the odds. Jiraiya could send Shadow Clones to give Tsunade reinforcements, and if Orochimaru or Jiraiya finish their fights before Tsunade loses then they can come to Tsunade's aid. She'd at least be great to stall Onoki so he doesn't team up with either Ei or Gaara to play the numbers game against the Sannin.
Round 7: the edo Kage (they are alive)
Wow, 3 against 4 again, but this time more powerful versions of the previous 4. The gauntlet may end here for the Sannin.
Round 8: KCM Naruto and MS Sasuke
If the Sannin do make it past Round 7, I could actually see them winning this.