You have to create separate listings for each site as the formats and categories are not the same unfortunately.
If I try to use 'create similar' from a UK listing the ebay site dropdown menu is greyed out and stuck at the UK site.
From 'create new listing' the drop down menu option at the top right of the 'Create an ebay listing' screen should give other countries.
I would expect once you have created a US format listing you could use 'create similar' to create further US site listings from it.