Stana Katic and Nathan Fillion

Now that Richard Castle's first Nikki Heat novel is getting the movie treatment within the ABC series Castle, TVGuide.com hit the set to find out who Nathan Fillion and Stana Katic think should play Castle and Beckett in the film.

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"I'm of a couple of different minds," Fillion says of who should play the novelist-turned-crime fighter. "I think we could go a couple of different ways. One, Daniel Craig; then, in some kind of an off-beat casting, Elijah Wood. I think that he would be really good, and I've always been a really big fan."

As for who should play Beckett, Fillion thinks Scarlett Johansson.

"She definitely is bodacious and voluptuous," Katic says with a chuckle.

Katic has a few other possibilities in mind. "Cate Blanchett. I think she could kick some butt. You know who else is really lovely? Rachel McAdams. She'd be a really sweet one."

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As to who should play Castle, Katic says, "If it's Rachel McAdams, I think Tom Hardy would be awesome. He was pretty wicked in Inception. If it's Cate Blanchett, Robert Downey Jr."

"Or it could be Angelina Jolie and George Clooney," Katic adds, followed by a cheeky "Mmmm."

"That would be a big box-office draw," Fillion agrees.

Co-star Seamus Dever, who'd love real-life friend Zachary Quinto to play Detective Ryan in the movie, revealed that Desperate Housewives star Kyle MacLachlan could be a front-runner for Richard Castle.

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"Nathan is very good about casting out the net and asking his friends or people that he's worked with to come on our show," Dever says. "Nathan put it out there, and Kyle was like, 'Sure, I'd love to.' I pitched to Nathan that he should play Castle. They're a lot alike: Handsome, great head of hair.'"

Who do you think should play Castle and Beckett?