I know better, really, and for years have been appreciating that I can have three Thanksgivings in some years: Canadian, American, and English Christmas, nicely spaced out at 4-6 week intervals so I have time to recover. Further, at least I *can* buy fresh cranberries for American Thanksgiving these days, as opposed to my first year or two back in the UK, when they weren't available.
But there's a reason that the Thanksgivings are when they are, and they contain the food they do. They're harvest festivals, and most of what's traditionally eaten is seasonal. That includes the cranberries, which are harvested in September through November.
I only just looked up when cranberry harvest season was. That's because I just cooked cranberry sauce to go with an English Christmas meal, and the cranberries were really not as good as they usually are - not as juicy, not as flavorful. For the first time, I needed to add water while making cranberry sauce; the berries were not self-sufficient that way. It made me wonder if they were past their season, older cranberries.
So that's the downside of celebrating in December with cranberries in the UK: by the time they're "in season" in the shops, they're out of their growing season already.
That said, I have every expectation that the meal(s), on the whole, will be as spectacularly good as usual.