Definitely not. The casting of Ryan Reynolds as Deadpool happened in the film versions. The comic had its own set of creative teams and no direct connection to his casting.
It's hard to say for sure. Sometimes the cast's schedule and availability determine if they'll attend Comic Con. Keep an eye on the entertainment news for updates.
I don't have that information. But you could follow the social media accounts of The Flash or Comic Con for any possible announcements regarding the cast's presence.
Riverdale is primarily based on the Archie Comics series. The show takes elements from the classic comic characters and storylines and gives them a modern, darker twist. It incorporates various relationships, mysteries, and coming-of-age themes from the source material.