I’m not familiar w/ this actor, so I don’t really have any strong feelings about the casting. What I do like about this, though, is that hopefully it means we’ll finally be getting more casting updates about the show soon. Can’t wait to see who they get for Jessica and Sinestro especially! 
I didn’t like him on American Horror Story: Freakshow…but then again, you weren’t supposed to like him, so kudos to him on that. After watching the new Mortal Kombat movie, I would’ve loved for the guy who played Kano to play Guy. It was a very similar tone.
That being said, let’s see what Whitrock can do as Guy and what layers he can bring. Whenever people think of Guy Gardner, it’s always his brash personality, but he’s got layers to him and Whitrock is a good actor.
I’m not familiar with Finn Wittrock. I can say that from his picture he does looks like Guy!