jp1822 said: "And of course, operating a private rail car with a Renaissance consist is not possible, , , "
This is not true, because of course the Renaissance "Ocean" runs with a Park Car on the tail. Via has "transition Renaissance cars" which attach to the Renaissance train set, on one end with drawbars (or whatever), while having a traditional coupler and diaphragm on the other end to attach to 'traditional' cars (I suspect that the baggage car, at the head end of the consist, has a similar treatment). For some unexplained reason, that 'transition' car (between the sleepers and the Park Car) contains nothing for the passengers, no seats, no bedrooms, just a long, empty carpeted room, with two mechanicals cabinets and with the windows covered. On the other hand, whether or not Via would run that car on the tail of a Renaissance train set for the sole purpose of attaching a private car is a separate question.
Nevertheless, I do believe that Via does now ban attaching private varnish to Park Cars. I'm not sure if that's due to public presure or just not wanting the bother; my experience with Park Cars is that the observation seating area is rarely populated except when it gets too dark to see out from within the dome.
I would like to thank all the contributors for the answer to my initial question and for photo attachments. I invite you all to read my "Wisconsin to Nova Scotia to Montreal and Back" Trip Report, in that section of the Forum.