USA Network is developing the pilot, produced by Denis Leary and based on the short-lived Channel 4 series.
The new version will relocate the story of three paramedics from Leeds to Chicago, TVLine reports.
Mosley - who has appeared in Pan Am and the final season of Scrubs - will play EMT and sports fan Johnny, while Daniels has been cast as his best friend Hank.
Kevin Bigley (Game Change, The Dilemma) will play Brian, the youngest member of the trio, who still lives at home with his parents.
The role of Theresa, a savvy cop who is still attracted to her ex-boyfriend Johnny, will be played by Australian actress Jessica McNamee (The Vow, Home and Away).
Denis Leary insisted back in July that his version of Sirens 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."
> Sirens dropped by Channel 4 after one series
> Only Fools and Horses, Misfits: The British invasion of US TV
Watch a clip from the original Sirens below: