Ottawa! Come couchsurf at my place! PM me for all the details.
I have gone from Toronto to Vancouver PLUS more on the train and I have a love-hate relationship with VIA. I did half the trip on comfort class and the other trip on VIA1 because I went with my grandma, who couldn't handle comfort class for that long. VIA1 is WAY MORE but boy is it worth it, showers/food etc. etc. It was really awesome, but yeah, extravagant and something I don't think I would've done if my grandma wasn't there.
One thing about the train, you have to assume at least one of your trains will be late and it will screw all your plans up. The problem is, you don't know which one... this is where the love/hate relationship comes in. One of our trains abruptly lost power for about four hours and everything was all wonky after that. Another time, we were stuck in the middle of Saskatchewan for a few hours in the middle of the night, creating more wonkiness... but that's all part of the experience right.
It takes three days, if I remember correctly, just to get out there, so I dunno where you should really stop. I didn't stop in Winnipeg, but I stopped in Banff, Jasper, Lake Louise, all very nice places. I think if you have already been to these places, it would be nice to stop in either Regina, Saskatoon or Edmonton. I liked Edmonton and also Regina, but I didn't go to Saskatoon...
I also went all the way to Prince Rupert and Prince George, but I wouldn't recommend this, it was very far and really boring. Also COLD!!!
I would say you should definitely go further along the rail line to the east coast! You can't miss Halifax, there's lots of history there, and the ocean is beautiful of course. Try for Peggy's cove, and visit my best friend who is in the RCMP there! Ha!
Let me know if this helps. Ask me more questions, etc. etc.
Oh and also, I'm a super expert on Niagara Falls, I lived there for the first 18 years of my life. I also know quite a bit about the Windsor-Quebec City corridor, so ask away.