Late November can be anywhere from +10 to -20C across most of Canada. It just plain depends, as it's so hard to predict anymore. I mean, this past week was near +20C most days, which is warmer than normal.

I'm not sure how well the train runs from Western Canada into Toronto, but my dad took the train from Halifax to Toronto in July (it was free for current and retired military), and it started with a 3 hour bus ride to meet the train, then a 5 hour wait for them to add some cars, and missed connection in Montreal. The crew indicated it was normally messed up on that run, so hopefully coming from the west is better. I personally would just do as mentioned above, and go Vancouver to Calgary, fly into Hamilton Ontario, go to Niagara for however long, then back to Toronto and carry on east from there at whatever schedule suits you. Train travel in Canada isn't cheap either. You'd probably be further ahead flying from Calgary than paying the extra train fare into Ontario, and be there in 4 hours instead of days.