Could you please give a little more detail as far as the difference in a YUpper berth, Lower berth, and cabin for one? Do they all have big windows like Amtrak roomettes? Aren't some of them just separated by a curtain? I have been told I snore loud which should I get so as not to bother other folks? Is the endpoint at TWO and Toronto union station the same place? How hard is it to get from there to the actual Niagara Falls from there?
An "open section" consists two seats facing each other by day. The person with the lower berth has the seat facing forward, the person with the upper berth has the seat facing backward. The upper and lower berths can be sold separately to single travelers. There is a full floor-to-ceiling wall between it and section ahead or behind it. The section is completely open to the aisle during the day. There is a window in the section.
At night, the seats convert to the lower berth, and the upper berth is folded down from the the ceiling/wall above the window. Heavy, blackout-style curtains are hung between each berth and the aisle. At night, the lower berth has the section's window, the upper berth is windowless.
As we've mentioned, the scenes on the train going from Chicago to Florida in "Some Like It Hot" have a very accurate depiction of open sections (although the number of people they stuff in the upper during the "party" seems a bit much). Go rent or stream "Some Like It Hot" and you'll understand pretty much all there is to know about open sections.
What Via calls a "Cabin for 1", a roomette, is completely private for a single traveler, with a chair during the day and a bed that folds down at night. It also has its own window.