Probally a Cattleman since it's his default.

I would think a cattleman or schofield

Arthur does not have a "cannon" sidearm. It is entirely up to the player.

In my opinion, Arthur likes to keep trophies, so I imagine his canon revolver would be the best one he picks up from ‘the noblest of men, and a woman’

Jim boy Calloway’s schofield, or whichever one you prefer

The way I see it, there’s two ways of looking at it

Video game collection Arthur who has two types of every possible sidearm, each fully upgraded and made of solid gold (unlikely)

Or Character Arthur who would just stick with a cattleman revolver because he’s not one for style or flash.

In my opinion, he just keeps the starting Cattleman as his main arm, and switch off hand sidearms with whatever powerful revolver or pistol he finds or buys at the time. So for example, when he finds the Schofield revolver in the Odriscal business in valentine, he uses that as his off hand weapon until he finds another weapon he likes.

And at the end of the game, his classic cattleman is all fancy looking, maybe with silver plating and the heroes pearl grip (which I might add, is only available for the cattleman.)

It’s spelled Canon and it’s a black steel schofield revolver, you can tell from concept art and trailers

Sorry only colonel daren has a cannon sidearm. although it would be cool if you could get one.

Cattlmen which has a special arrangement and has its own carabine repater

Callaways Revolver is my canon choice as Arthurs primary sidearm while the Vulcan pistol the secondary sidearm