VIA Rail
Presently, VIA Rail Canada service runs from Toronto to Montréal along the North Shore of the St. Lawrence River, and service onward to Québec via the south shore of the St. Lawrence. Service through Ottawa diverges at Brockville and rejoins at Coteau. This proposal would add two new routes to the network - Toronto to Ottawa via Peterborough, and Montréal to Québec via Trois-Rivieres. Modest service improvements would come to the existing routes, but these new routes would be largely free of freight train traffic and excellent service levels could be offered.
This would be really good for passengers travelling between the largest cities (Toronto, Ottawa, Montréal and Québec), while still preserving service to medium-sized cities like Kingston and Brockville. This is key, as a seat that turns over at Kingston is a seat that is being paid for twice.
This isn't French-style high-speed rail, but given that Q2 2018 was VIA Rail Canada's 17th consecutive quarter of ridership growth, it's clear to me that mega-projects aren't always the right tool to build ridership and shift people onto more sustainable means of travel.
If you need to get from, say, Toronto to Windsor - a route I know very well - as fast as possible then flying is an option. There are 4 daily Porter Flights from Billy Bishop, and 4 daily Air Canada Flights from Pearson. The train's strengths are in its ability to serve multiple travel markets in one run. The Toronto - London business traveller, the Woodstock - London - Chatham day-tripper, and the London - Windsor student traveller are all served by one train. All this is in addition to someone going all the way from Toronto to Windsor.
Why not play to your strengths?
With all that said, there is one issue that needs to be mentioned. The Mount Royal tunnel in Montréal used to be how passenger trains along the north shore of the St. Lawrence accessed Gare Central, but it is being converted to accommodate automated light rail trains. This means that in the interim, north shore VIA Rail trains won't be able to get downtown - passengers will have to change at an uptown station. This will be resolved as we complete the move towards a next-generation signalling system, but this underscores the need for a national transit strategy.