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.
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.
If you want the clearest chapter reference, go to Chapter 221. Early on, Many agricultural students found themselves with tears brimming in their...; later, the chapter leans on Great, the hardships of agricultural students have finally been discovered..
Chapter 232 is the strongest chapter-level answer because it starts from But soon, she suppressed this strange feeling and slowly began to speak,... and follows through on The moment he saw the information come through, Jiang Li fell silent..
A practical answer is Chapter 257, because it turns the idea into a concrete scene. The chapter opens with This nation seemed to have a particular love for bright colors., adds pressure through After a round, Jiang Li's head was already filled with various kinds of..., and ends on Yet in the end.
A practical answer is Chapter 233, because it turns the idea into a concrete scene. The chapter opens with [What the hell, what's this about life span ending??, adds pressure through Haven't you already exposed all my secrets?" "But..." Jiang Li rubbed his..., and ends on After all, a real big.
Look to Chapter 232 for the clearest answer. It begins with But soon, she suppressed this strange feeling and slowly began to speak,..., keeps building through I'm the oldest, so I should get this chance!" "Get lost, I'm the youngest..., and lands on The moment he saw the information come through.
The best chapter pointer here is Chapter 256, "Bonfire Feast". It opens with Turning around, Jiang Yan and Zhao Lang found their heads had been... and closes on I was dazzled seeing Jiang Li trending today." Next door, Su Yinwan let....
The best chapter pointer here is Chapter 221, "No Choice, He Gave Way Too Much". It opens with Many agricultural students found themselves with tears brimming in their... and closes on As a result, the production crew of Shanbian Company was frequently....
A practical answer is Chapter 233, because it turns the idea into a concrete scene. The chapter opens with [What the hell, what's this about life span ending??, adds pressure through Haven't you already exposed all my secrets?" "But..." Jiang Li rubbed his..., and ends on After all, a real big.
Look to Chapter 238 for the clearest answer. It begins with Jiang Li was actually first on all three leaderboards?!, keeps building through Could it really be that outrageous?!, and lands on And, to Zhou Xu's alarm, they did find a problem..
The best chapter pointer here is Chapter 237, "Top of the Three Lists! Truly Deserved!". It opens with It seemed as if, believing the spilled water couldn't be recollected, Ah... and closes on The netizens responded in chorus, and no one insisted on forcing Jiang Li....