First, looking at the eastbound schedule, this appears to be the way I would travel to see most of the best scenery with the Canadian's new schedule. You are likely to get most of the Canadian Rockies, that are often over this route. I'd be curious as to what they do at Winnipeg since you'll be arriving around 22:00(?), but won't be let back on until around like 23:30. Do they allow people to stay onboard now and sleep if travelling eastbound? Everyone used to have to "get off the train." But that's kind of a late time to be boarding. Boy how I wish they would bring back a train from Winnipeg to Vancouver via Calgary, Banff, Lake Louise etc. VIA Rail likely has the equipment to make this happen - or at least they had the extra equipment when the previous Canadian schedule was in place (where it could operate with just three train sets, but now requires four under the current schedule). If you can wake-up to see the scenery from Parry Sound into Toronto, it offers some nice views! Through Ontario (the Canadian Shield and the Praries) - not sure what the main scenic highlights would be. I always liked the scenery from Sioux Lookout into Winnipeg, as it offered some nice "rock" scenes scattered with lots of lakes! I am sure other sections that are now daylight running offer good scenery.
As for your specific question on the Skyline Dome Car:
Assuming you'll have two Skyline Dome Cars and one Park Dome/Lounge Car:
- the first Skyline Dome Car is largely (or sometimes exclusively) for economy/coach passengers. And sometimes this is where economy/coach passengers go to get their snacks and also have their meals, as 1/2 of the lower part of the dome car is a lounge, and 1/2 is set up with tables and chairs like a mini Diner. For example, on the Montreal-Gaspe train, the Skyline Dome Car is all that is usually offered to sleeper and coach passengers for meal/food options. I believe most Skyline Dome Cars are equipped with a kitchen, then there's a snack bar area next to it.
- the second Skyline Dome Car in the Canadian consist is often touted as the "Activity Car." It is here that one can play board games, watch movies, or even have an "onboard activities coordinator" plan different events for sleeping car (aka Tourist Sleeper) passengers etc. Also this is the area that you would go to try and buy souvenirs. This Skyline Dome Car is located right next to the first Diner, as typically the Skyline Dome Car and Diners are coupled together. Seats in the dome are first come first serve!
- The Park Dome/Lounge Car is where I would try to get a seat (in the dome). This car features a lounge in its bar/snack bar area, then a "bullet lounge" with lounge chairs as the rear signature car of the train. Upstairs is where they have seating in the dome section. You should be able to get a seat here without much trouble. I've never had trouble trying to get a seat in the dome of the Canadian. Typically those passengers assigned to the rearmost 3 sleepers use this dome. They also offer tea and some general snacks in this car (they may in the other Skyline Dome Car as well). Again, as the rear car, including a dome, this car is really a my favorite for watching the train move forward over the landscape and then one can often turn around and see the receding tracks of where one came from!
Take a look on VIA Rail's web site for some pictures of these various cars.
Yes, VIA is much more flexible with adding and subtracting cars either at Vancouver, Toronto, or even Jasper than compared to Amtrak. This is because VIA Rail has the equipment available to do this. Amtrak is strapped for equipment! Also notice the ratio of sleeper cars to coach cars on the Canadian - especially. Even the Ocean outnumbers sleeper cars to coach cars. In peak season, one can often see the Canadian operating with three coaches, and then 20+/- sleepers! Course the train does shrink during off-season, typically the winter season. And this is when VIA will often add/subtract cars from the Canadian at Jasper. Not only is this cheaper for VIA - as they also pay the host railroad a "per car cost" to operate cars over a line, but it also makes the best utilization of sleeping cars (short turning them to meet demand/supply over portions of the line they are needed the most).
** The above assumes you will have at least two Skyline Dome Cars and then the rear-most car being the Park Dome/Lounge Car. How they setup the consist in between the last Diner and the first Skyline Dome Car kinda depends, as it is towards the front of the train tha sleepers could be added/subtracted at Jasper.
*** Open to corrections on this post based on curretnt operations of the Canadian during this time period, as I haven't been on the Canadian since it changed its schedule.