To increase frequency, sure. To interweave high speed rail (defined as 250kmh+) with 'regular speed rail, including freight, I don't think happens anywhere in the world.
Yes. I personally don't think we should be looking to emulate Europe because they European rail network is designed with passenger primacy in mind. Our network is far different. My vision is for something similar to Amtrak's corridor service.
Perhaps using the abandoned line would be suitable, perhaps they could use the existing CN/CPKC owned lines and improve their service delivery and execution?
I forget the details but VIA paid CN to add extra trackage somewhere in the Corridor in eastern Ontario. CN charged an exorbitant amount for the job, claimed it as part of their infrastructure (it's on their property after all) so the end benefit to VIA was limited.
One thing I have thought about is building bypasses of towns that loop around cities, towns, industrial sites, railyards and dense areas of known congestion. Here is a great example of one such recent development:
news.ontario.ca
A 15 minute time savings by simply avoiding running your passenger train through a railyard, a novel idea (sarcasm).
Now, VIA has their new Siemens 'Venture' trainsets. CN claims they are too light and too short to consistently trigger their signalling systems at speed, so has limited them to low speeds (40mph if I recall) at crossings. In response, VIA has doubled-up their sets to satisfy the minimum number of axles that CN demands.
When the original proposal was high frequency rail, the Toronto-Ottawa routing was proposed along the abandoned Quebec-Ontario (CP) ROW that runs through Peterborough. With a few alignment changes, it was largely felt to be suitable. Now that it has morphed into a high speed project, I highly doubt much of the ROW will be considered suitable.
The biggest issue I see is the problem known as "first mile/last mile phenomenon" and how to solve it. We see this with air travel in Canada:
If my choices are fly or use an automobile, I will quite often choose automobile, unless the distances are extreme. It's simple really:
Let's say I were to travel to Toronto from where I live. It's 800km door-to-door give or take, so roughly a 9-10hr car ride given I will stop and eat, get gas, stretch, traffic, etc.
Now on a standard short-haul flight on a Dash 8, you'll achieve a cruising speed of 600km/h give or take but with the amount of screwing around you have to do to get on that plane, it quickly makes it not worth it to choose flying over driving:
2hr commute to the airport
Arrive 1h30min early to check-in, deal with luggage, clear security, etc.
30min to board, taxi, takeoff
We haven't even left yet and I could have been halfway to Toronto already.
1h30min flight
30min to taxi, get to the gate, disembark the aircraft
30min waiting for luggage, getting rides, etc.
Now you are 6+hrs in to your journey on a vehicle that travels at 6-7x the speed of an automobile and you aren't even at your destination yet.
You spent way more $$$$, and arrived at your destination at basically the exact same time with negligible benefits to convenience and very little in the way of time savings.
The same scenario applies to rail travel in North America.
My solution to this would be to completely separate the long-haul and short-haul rail networks. Right now, every Train going in to Montreal/Toronto flows in to a central station. I would keep the Central Station as a distribution link for all the short-haul connector routes serviced by municipal/regional carriers but then build a dedicated station outside the City Limits with the sole purpose of dealing with long-haul carriers.
You could link these stations with a branch line to the central station, much like Union Station is connected to Pearson via the UP Express, which is a 28min journey from downtown TO with departures every 15 min. It wo
This is where HFR comes in to play:
HFR would be exclusively long haul and would have minimal/no stops between major metropolitan areas. HFR wouldn't be true hi-speed but speeds of 200km/h should be what can be achieved.
You could travel 90% of the distance from the GTA to Ottawa in 2hrs and then add an hour or two on either side the final 10%.
You now have a service that is comparable in time to automobile travel, maybe even slightly faster, far safer, probably cheaper for your pocket book and is more convenient than Air Travel.