the salary cap increase is not

Short answer no. The cap although not confirmed is reported to go up around 1m. ROR may be a possibility but running only 1 extra on the roster would be terrible long term for the Leafs especially for the full season.

I don't think it'd be smart for Toronto to re-sign ROR to be honest, but he's a great player you never know.

Someone told me 3 mil and I saw an NHL article saying it will increase by 3 mil

I found the article again here
https://www.nhl.com/news/nhl-salary-cap-could-increase-by-at-least-4-million-in-2023-24/c-336522332

Don't think they resign him if he wants 6m, chances are that he goes back to the Blues and resigns for that x2 or 3. or he signs for like 3-5m in Toronto x1 or something.

He originally showed interest in Toronto because he grew up near Toronto ad has relatives near Toronto. I will say (if I do this again) he signs a 2 year 3 mil Contract so we get like 3 mill in extra cap to sign someone else or even better keep Kampf

Yeah, Leafs may not want to keep him. Although if Dubas is still the GM I would expect him to resign him. I don't think the Leafs need Kampf with O'Reilly+Holmberg, but if he's cheap enough maybe. I also think that the Leafs will use the saving to sign a guy to a prove it deal that could potentially play at 2LW depending on how Knies does.

O'Reilly won't be 6mill to re-sign, unless he goes on an absolute tear with the Leafs.

I'd say 4.5mill x 2 years is realistic