You are not assigned a seat by number (at least last year when I did BC on the Starlight). You are just guaranteed a seat.

As far as claustrophobia goes, seating is similar to regular coach, perhaps a little nicer. We sat on the lower level. I don't really know if its any better or worse than a roomette other than cost and meals included in your fare. In BC you do get a voucher which may be used in the cafe car or diner and, IIRC, the cost of wine tasting in the PPC. A roomette will give you a bit of privacy that business class won't.

John