Further to the previous post, continued digging on the matter of ownership of the USRC as that pertains to air-rights, Union Station and shed land ownership and other matters, it's difficult slogging, a lot shows, but interpreting it and not having more recent court decisions and/or precedents hinders knowing the legal status, but just found this:
[...]
...the Canadian Pacific Railway Company to the use of portions of the bed of the harbour on which they had laid their tracks across the prolongations of the streets mentioned, a grant was made to that company by the Dominion Government of the "use for railway purposes" on and over the filled-in areas included within the lines formed by the production of the sides of the streets. At a later date the Dominion Government granted these areas to the city in trust to be used as public highways, subject to an agreement respecting the railways, known as the "Old Windmill Line Agreement," and excepting therefrom strips of land 66 feet in width between the southerly ends of the areas and the harbour, reserved as and for "an allowance for a public highway." In June, 1909, the Board of Railway Commissioners, on application by the city, made an order directing that the railway companies should elevate their tracks on and adjoining the "Esplanade" and construct a viaduct there.
Held, Girouard and Duff, JJ. dissenting, that the Board had jurisdiction to make -such order; that the street prolongations mentioned were highways within the meaning of the "Railway Act"; that the Act of Parliament validating the agreement made in 1892 was not a "special Act" within the meaning of "The Railway Act" and did not alter the character of the agreement as a private contract affecting only the parties thereto, and that the Canadian Pacific Railway Company, having acquired only a limited right or easement in the filled-in land, had not such a title thereto as would deprive the public of the right to pass over the same as a means of communication between the streets and the harbour.
[...]
I'll add more in quotation:
http://scc-csc.lexum.com/scc-csc/scc-csc/en/item/9855/index.do?r=AAAAAQAKUGVyc29ubmUgYgE
At a first glance, this appears more than profound! Haven't even begun to read this in detail, but it offers the City an interpretation of "bridging" the USRC for Rail Deck Park. I realize the point is relevant to more than just Union Station, but unless some of these earlier judgements were rendered moot or not-pertinent in later rulings, things are about to get very interesting as the City digs on ownership of the USRC and adjacent properties. (Edit: Note use of the term "possession" not "ownership" in reference to the railways)
Edit to Add: Can't quote due to copy-block, but the "Tripartite Agreement" (also referred to as "Esplanade Agreement") described at:
https://books.google.ca/books?id=BupHAQAAMAAJ&pg=PA572&lpg=PA572&dq=Esplanade+or+Tripartite+Agreement&source=bl&ots=1q9Pyh4ENJ&sig=B_54nS2NfC0ZCshhgm5qZje8RhQ&hl=en&sa=X&ved=0ahUKEwjzrZ2slM7PAhWo34MKHRFMD7cQ6AEIKDAC#v=onepage&q=Esplanade or Tripartite Agreement&f=false