Leary's USA Network version of the Channel 4 comedy was first announced in June 2011.
"We're still casting the pilot for Sirens," he told Vulture. "We haven't picked anybody yet, and the earliest we can shoot is August or September.
"It's going to be all unknowns [in the cast], so it's pretty exciting. I want the show to be all new talent. We're looking at all the actors in New York first, and we're setting it in Chicago, so then we'll look at the actors in Chicago."
Leary added that the Sirens remake will be "very different" from the UK original.
"The only thing that's similar is that it's about this group of EMTs," he explained. "It's got some of the same feel, but ultimately, it's a different show. I hope it's good. I hope it works. I hope it ends up on the air."
The UK Sirens - which starred Games of Thrones actor Richard Madden - was cancelled by Channel 4 following a single series.
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Watch a trailer for the original Sirens below: