I think Orochimaru would be the most unexpected sensei. Usually, he's seen as a villain, but in a fanfiction, if he were to train Naruto, it would be extremely unexpected. He has a vast knowledge of jutsu, especially forbidden ones. He could teach Naruto some very powerful and unique abilities, but at the same time, Naruto would have to deal with Orochimaru's morally ambiguous nature.
Probably Tenten's sensei, Might Guy. It would be unexpected because Naruto is not really associated with the more physical and taijutsu - focused training that Guy is known for. But if Guy were Naruto's sensei, he would push Naruto to his limits in terms of physical strength and endurance. Naruto might also learn some really flashy taijutsu moves that are completely different from his normal combat style.
The most unexpected sensei could be Hinata's father, Hiashi. Hiashi is a very traditional and strict ninja. If he were to train Naruto, he would likely enforce a lot of discipline and propriety. He could teach Naruto some of the Hyuga clan's secrets, like how to better use his chakra control for precise attacks. This would be a huge departure from Naruto's normal, more free - spirited training.
Look to Chapter 205 for the clearest answer. It begins with Ah Fu had no idea what the video Jiang Li mentioned was., keeps building through He had been smugly thinking that the older sister was merely trying to..., and lands on Having such a sister certainly would bring happiness..
A practical answer is Chapter 227, because it turns the idea into a concrete scene. The chapter opens with Your Four Pillars of Destiny is very strong, with wealth, authority, and..., adds pressure through As long as you're in that house, they will never be at ease;
Chapter 215 is the strongest chapter-level answer because it starts from Jiang Li let out a light sigh and tried to adjust her posture. and follows through on He originally just wanted to see if there was a chance to complete his....
Look to Chapter 212 for the clearest answer. It begins with Although she appeared outwardly flattered, in fact, her heart was already..., keeps building through Since Shang Shaojing wanted to use his good score to help her restore the..., and lands on Suddenly, in an instant, his wildly beating.
A practical answer is Chapter 242, because it turns the idea into a concrete scene. The chapter opens with Just when Jiang Yan called to heaven and earth in vain, he looked up and..., adds pressure through Young Master Jiang, it sounds like someone is at the door, aren't you..., and ends on Just.
The best chapter pointer here is Chapter 265, "This Time You Must Help Me". It opens with As expected, the truth behind the video was unearthed one by one and... and closes on Miss Su, I also don't know why things turned out this way..." "Heh, you....
If you want the clearest chapter reference, go to Chapter 247. Early on, Facts have proved that arch-enemies often understand each other the best.; later, the chapter leans on It was barely dawn, and Jiang Yan had already had a meltdown..
The best chapter pointer here is Chapter 223, "Pigpen Live Stream". It opens with So, for the first time, Jiang Yan, who had always styled himself as the... and closes on The damned Jiang Li was tricking him again!.
A practical answer is Chapter 208, because it turns the idea into a concrete scene. The chapter opens with Jiang Yan clicked his tongue, "What's this about money?, adds pressure through After the staff counted, she had a total of 22 points, which was a..., and ends on Seemingly sensing the raging.