Most cross border tribes can cross freely. As far as I know, the Sinixt are the only ones who cannot. BC and Canada have a long history of denying the Sinixt ever lived here. As afr back as the 1890's (I think) there were calls to restrict their access to their territory. It is a very long and convoluted tale. I'm not sure if the governemnt were confused about who they were or intentionally ignorant. I lean towards the latter. It is not as if they were not told by anthropologists at the time.