As mentioned, the least amount of info White has given is in regards to the Pacific Northwest. All we know, and some of it being conjecture;
1) They're largely Buddhist
2) There is smattering of small fiefdoms, with which contain some of the largest cities on the continent, and are republics--remniscent of the Italian city states.
3) However, a larger, de-urbanized feudal state exists east of the Cascades, called The District of Columbia.
4) The population has a subtle Asian ancestry.
In general, this indicates an Anglo-Asian fusion culture. However, the Northwest is also the home to some of the most sophisticated and high profile Native American cultures. I like to think the indigenous culture has a large influence on the area. Interestingly, I was looking for "Native American armor" I found most of the high profile historical cases belonged to the Tinglit people.
Some of flourishes include using the faces of their ancestors, which is fairly unique for old world cultures, but probably simpatico the ancestor-worshiping east. (Mind you, ancestor worship isn't particularly a part of Buddhism, but it's very likely the Medieval American version is very much a Pan-Asian McReligion) Another interesting facet is that ones with metal have Chinese coins sewn in. Overall, this makes it the best blueprint for the gestalt of Asian, Indigenous, and Medieval influences. Also of note is many Tinglit artifacts have found their way as far as Russia, meaning the concept of a sort of Pacific version of Colombian exchange is already baked in.
Also of note is Tinglit people are Matrilneaer, much like the Secretarial states. Of course, they're very far, but it might be worth considering terms of models and divergent evolution, etc.