NB has reached consensus several times before that SM Hashirama stomps Itachi. But what about Base Hashirama? Can Base Hashirama beat Itachi with canon showings?
Canon showing means Itachi is as healthy as Kishimoto drew him in the manga, not fanfic Itachi with unlimited chakra
You do know Hashirama is on another level right? Ninjas in Hashirama's time are all stronger than ninjas in the time line Itachi and Naruto grew up in since they weren't really in war; they didn't grow up having to fight for their life since an early age against grown adults. Madara was taking out grown Senju adults before he got the Sharingan for example. Base Hashirama was fighting PS+full Kurama for a good amount of time and only went SM when he got serious.
As for Totsuka blade, base Hashirama catch PS slash easily so doubt Totsuka would hit him. Flower world have enough power to crush Finall Susanoo however Yata mirror would protect Itachi and have the wood go around him but then the pollen would make Itachi goes unconscious and the wood absorbs Susanoo chakra since it would be going around yata mirror and still trapping Susanoo. Hashirama is an expert at fighting Uchihas so don't see genjutsus working on him.
Itachi have low stamina, is sick, his MS cause his a lot of pain while draining a lot of chakra while making him more blind. Susanoo+illness is what killed Itachi so either Itachi kills himself or Hashirama will do it. Hashirama can also summon many wood clone and attack from all directions if he sees fit plus he had control of Bijuus 2-9 (2-8 before beating Madara).