Put a lot of thought and money into the wheels so you don't break down in the middle of nowhere. 26” is the norm for trekking bikes as they are available globally. 29” are becoming common and from what I read they are great for smoothing out a bumpy road.

In regards to buying a bike in North America, you should have no problem finding a reputable dealer in Seattle, Vancouver, Calgary or Edmonton. Just order what you need and do a mini tour until you are happy with your build.