John, I found two affixed metal stickers or labels on our trailer. They are screwed on right next to the door.
One says: "This vehicle conforms to all applicable USA Federal motor vehicle safety standards in effect on the date of manufacture shown above." You can see the date of manufacture was May 13, 1987. Why a trailer is called a motor vehicle I can't say.
The other label is from Oregon State. It reads: "The manufacturer certifies that this unit is constructed in accordance with applicable Oregon Statutes covering plumbing, heating, and electrical
installations in recreational vehicles." I don't know when this label was affixed to the trailer, but presumable when some previous owner imported it into the states.
Don't know if any of this info is helpful to you or pertinent to your case in that it sounds like you're looking for a newer model trailer. I'm presuming that this is the sort of thing that the border agents would look for upon importation to the states from Canada and I don't know if an older trailer like ours would be given more or less scrutiny. Good luck in your search!