The Once Upon a Time star told Digital Spy that he is a big fan of the ITV period drama, which airs on PBS in the US.
"I'm a huge Downton Abbey fan," he revealed. "In fact, I'd love to do an American [version of] Downton Abbey if I could possibly make that happen.
"I'm a huge fan of the show - the writing I think is fantastic. It's very hard for me to watch one episode and I sometimes have to skip ahead and watch two!"
Dallas - who appeared alongside Downton star Lesley Nicol in the second season of Once Upon a Time - joked that he could join the series as a relative of Martha Levinson (Shirley MacLaine).
"I could be like a cousin or I could be Shirley MacLaine's nephew coming over from America," he laughed.
Once Upon a Time returns to Channel 5 in the UK on Sunday (April 7) at 9pm.
> Once Upon a Time Josh Dallas: 'Charming, Snow's joy won't last long'
Watch the stars of Downton Abbey talk the upcoming fourth series below: