Is the casting of Wentworth Miller and Dominic Purcell together in "The Flash" intentional?

Question

I have recently watched Prison Break and am now watching The Flash. A couple episodes into the series, an antagonist (Captain Cold) played by Wentworth Miller (Prison Break's Michael Scofield) shows up. Later in the show, Miller's character is being supported by another person, Heat Wave, played by Dominic Purcell, the actor impersonating Miller's brother in Prison Break.

Was the cast of these actors planned as an Easter Egg, or was it just the luck of the draw that exactly these two team up in The Flash?

Additionally, in another episode of The Flash, yet another known face from Prison Break, Robert Knepper shows up as Clock King.

Answer 1

From comments made by Wentorth Miller to Buzzfeed it looks like he was, at the very least, instrumental in recommending Dominic Purcell:

Miller: During my first episode, in a conversation with [DC Entertainment’s Chief Creative Officer] Geoff Johns, he said, “We’re trying to cast this Heat Wave character. He’s this hothead, aggressive, unpredictable, force of nature. Are there any actors you can think of?” I said. “Dominic Purcell.” I was 90% serious, 10% joking, because I didn’t think they could pull it off or that they would even be interested in such a pairing — not knowing they were huge Prison Break fans. They must have made the call that afternoon.

Purcell: They did.

Buzzfeed: What did they say?

Purcell: Wentworth dropped me an email and asked if I would be interested and I said, “Fuck yeah!” To work with Wentworth again? Yes. I was just excited to see Wentworth. It wasn’t about The Flash; it was about reconnecting with him and having a blast. Now that I’m on the show, I’m very thankful that the show is the success that it is. I’m humbled by it, I appreciate it, I love the cast, and it allows us to be operatic. As actors, that’s all you ever really want to do: You want to go big!