Patrick Wilson
We’ve already seen Patrick Wilson as a good-natured DC comic character when he played Night Owl in Watchmen. He nailed that role, and was extremely enjoyable to watch. He doesn’t have blonde hair, but he has the likable manner and good looks that are essential for Flash, especially the Barry Allen version. Just look at him, that’s a face you know you can trust.
There’s a chance Zack Snyder will be directing Justice League, and he may want to find an actor he’s already worked with. While the opinions on Watchmen are polarized, Wilson and Snyder did make a good team, and it wouldn’t be a stretch to think Snyder would want to channel that again.
Another film that really illustrates how well Wilson could take on Flash is Insidious. While Insidious is nothing like Justice League, the way Wilson attempts to figure out just what is going on with his son and their house is a perfect display of the sort of intelligent yet vulnerable character that Flash is. Wilson absolutely killed that role, and would do no different as Barry Allen.