According to a posting by Brian Quinn - usually well informed - on several message-boards there could be different versions of the 'Christmas Duets' Album released in several territories; one for the U.S.A, one for the U.K. and one for Canada.
The localized versions should feature artists from the said country. The UK album will be released in November and there will also be a single release. No tracks or artists are known at present for the UK or Canadian releases.
Sony BMG apparently have high hopes for this album. Looks like we will all have to start saving up for the various versions.
Please note that the 'Christmas Duets' Album is different to the one tentatively set for 2009 which will be more eclectic in format and artists. There will be a major push for that release including a TV Show built around it.