The assertion that you just can’t regulate prices and you just can’t tell a company that someone else can’t use its infrastructure are answered by the telecoms industry, where nascent operators in the wired and wireless space have been given, by law, access to infrastructure, and legacy telcos obliged to do stuff like reduce contract lengths and port out numbers. Does this directly map to rail? No. But it shows that concepts are not unthinkable - especially when as noted above the existing CTA legislation contemplates some level of government mandate - that should not be considered as far as Ottawa may grasp. Also, the continued domination of the legacy telcos in both spaces (and AC/WJ in the airline market) are a sign that collapse into bankruptcy is unlikely to be the fate of the Class Is.
The difference with telecoms and airlines is that the benefits of deregulation/liberalization were widely understood and at least to some extent publicly desired, whereas passenger rail has been in decline for so many years, the public may not believe that it can get better.
A problem in comparing the Corridor with Calgary-Edmonton is that the latter is both the most theoretically promising corridor but also one wholly contained in a single province without a separate public service obligation which one could define for White River or Jonqueire, Even Halifax’s local service was posited as part of a service into NB. Accordingly, even absent a PRIIA type regime, many people simply think that it is Alberta’s to do, or Canada’s not to.