Looking at specific markets really shows you why stops need to be controlled.
Toronto-Ottawa: 130km from Toronto to Peterborough. 1.3 hrs at 100 kph. 290 km from Peterborough to Tremblay. 1.45 hrs at 200 kph. Assuming 5 stops (Eglinton, GTA East, Peterborough, Fallowfield) at 6 minutes each, yields 0.5 hrs. So 3.25 hrs total. This going to savage Toronto-Ottawa flying. Particularly when you account for the travel time from the airport to your destination. Having two train stops in Ottawa, both with decent transit connections, provides a huge advantage.
Ottawa-Montreal: 140 km to Coteau. 0.7 hrs at 200 kph. 65 km from Coteau to Gare Centrale. 0.65 hrs @ 100 kph. With Casselman, Alexandria, Coteau, Dorval, it's 0.4 hrs for the stops. 1.75 hrs total.
Using a similar estimation, Montreal-Quebec City gets a huge boost. It's 50 km from Gare Centrale to Mascousche via Laval. .5 hrs at 100 kph. And then 260 km from there to Gare du Palais via Trois-Riviere. 1.3 hrs at 200 kph. Add 0.3 hrs for stops at Jean-Lesage airport, Trois-Riviere and Laval. 2.1 hrs total. Incredible compared to the 3.4+ hrs from today. Trois-Riviere to Montreal is 1.25 hrs by my estimate. Commutable.
About 5 hrs from Toronto to Montreal via Ottawa (gonna assume some efficiency makes room for the Ottawa stop). The math above shows you why controlling the number of stops, particularly on the Ottawa-Montreal leg matters. Also shows you how limiting the urban areas are and why more investment on grade separation won't pay off. Making the 200 km stretch from Peterborough to Smiths Falls fully grade separated to enable 250 kph operation, saves 0.2 hrs.
There's one stretch where the payoff on grade separation is big: Ottawa-Montreal. Speed up the Ottawa-Coteau portion to 250 kph and limit stops to Alexandria and Dorval and it's now a 1.41 hrs trip. Effectively commutable. And gets Toronto-Montreal down to 4.66 hrs. 4 hrs 40 mins to Montreal consistently would be substantially competitive with driving and bussing.
I really do believe there's an investment case here. Once you start looking at the numbers and become judicious on where large upgrades are warranted and where stops have to be allowed. I am also hoping that institutional investor involvement will bring in a more ROI-focused approach on stop placement.