Not even local GO trains run that frequently

For whatever reason, GO operators have trouble envisioning a system that is useful for anything besides commuting. This is a entirely separate project.

when there is no decent public transit on either end?

What are you talking about? Ottawa's station is directly adjacent to Tremblay, Montréal's Laval will be Lucien-L'Allier or Gare Centrale and De La Concorde, all right on the Métro, Toronto's goes to Union or a future East Harbour station, Toronto's transit sucks for the city's size but there is genuine ongoing work, projects large and small to improve it.

This will piss away tens of millions in feasibility studies

The feasibility studies are already done, multiple times over, the current step is the Environmental Assessment and design which is a precursor to actually building the thing instead of thinking about it.

get progressively less affordable

That's always the price of waiting/delaying, it's always more expensive than announced, at minimum due to inflation but also loan interest, so suggesting to not even try will make a project more expensive if we start again from the pie in the sky stage (we're currently past that). And I think we need to swallow the pill of the full construction cost early, be it through public bonds or financing. We see from the example of California HSR that flying by the seat of their pants on funding has been a huge source of delay and budget ballooning.

governments kicking the ball down the road

I do worry about 2029 where even if construction does start, the next government underfunds or intentionally slow-walks construction, in order to manufacture justification to cancel the project.