Game Of Thrones: 9 New Characters Set To Appear In Season 7
5. Merchant
Description: Merchant, in his 40s. HBO wants a character actor for this part. He’ll appear at an inn during a busy evening. They’re open on his race and appearance. He’ll shoot scenes during the first week of November.
Who It Could Be: This one is left very open, but the fact that they're not concerned about race here opens this up to locales beyond Westeros, so this could be a merchant over in Essos - Braavos and Volantis are both locations that qualify as the sort of places you'd find a merchant at an inn.
If it is either of those, then we'd likely be looking at someone who interacts with either Jorah, if he goes off around Essos in search for a cure (or just to drown his sorrows while he still can), or Tyrion, if Daenerys and co. happened to stop off at Volantis on the way back to Westeros (though I'd expect her to go straight there).
If the merchant is in Westeros, then it'll probably Dorne or, most likely, Oldtown, where a merchant would likely appear to sell his wares, and maybe bump into one Samwell Tarly.