I'd give the slight edge to Dubois because I think his straight right hand would find the target quicker than Cooney's left hook. Cooney also never beat any relevant top 10 Heavyweights where as Dubois has numerous wins over relevant top 10 Heavyweights. I'd go with Dubois by KO because I think he's a bit more proven overall.
We don't know how good Cooney could have been but probably Debois as his intangibles are more proven.
Dubois is something of a glass cannon, so he cannot be a prohibitive favorite, but his wins over Joshua and Wardley are better than anything that Cooney showed us.
I would favor the more proven Dubois but also think Cooney could just blast him out of there in a few rounds if he manages to not get pole axed in that period of time.
Cooney. By the time he faced Holmes, he was a fairly solid fighter. He was moving well for a big man, had a solid jab and was capable of dropping in the odd right hand as well as his famed left. Holmes often had to use offense as defense for large portions of the early stanzas, to keep Cooney at bay - which he did quite brilliantly. Dubois has a reasonable jab and good right hand, but he's not particularly fast and his accuracy and timing runs a bit hot and cold. He also doesn't really have a lot going for him defensively. Cooney W KO 3
Cooney was a better fighter but both had the power to knock each other out and neither had the best whiskers. anything can happen in a match like that