This is why I think all rail lines need to be Nationalized. Then you contact the various freight operators to run on it.
There's already the power under various Acts, notably the Transportation and Crossings Acts, for the Feds to intercede in specific situations to impose improvements, sharing of track, and relocation of track. There is absolutely no need to "Nationalize". What's bizarre is that the Feds haven't acted to make the 'The Missing Link' happen, or to announce a scheme to involve the private sector into doing it. There may in fact be actions on-going behind closed doors. For the sizable if not massive cost of doing this, it would pay for itself many times over, and render the GTHA vastly more efficient and safe for freight handling and movement too. This has been done in various other Cdn cities, and on a large system-wide basis in Ottawa via the NCR (The National Capital Act helped, but the power was already extant in various railway acts). It's not like this is unprecedented in Canada.
CN didn't offer it, nor will they. Until the bypass is built, there is precisely 0 incentive for them to do anything with the corridor - which also happens to be the percentage chance that Metrolinx has of buying the line from CN until the bypass is built.
Indeed, and as much as the Feds could force the issue, much better to use the carrot than the stick, and that's to push for a consortium to build The Missing Link, of which CN and CP would be welcome to join. It's a win-win-win situation for all concerned if presented the right way. The irony is that the funding isn't really the problem. It's setting up the business model that is. There's massive amounts of off-shore cash looking to invest in Cdn rail infrastructure. The devil is in the details. CN and CP can either get in front of this, or be left behind and have to accept a much less appealing option, one of which is once built, the Feds then dictate that it be used. In all likelihood, that would be implicit in the business model to placate investors. Unlike a number of other posters, I disagree that CN and CP would have to have their own tracks. The tracks could even be a third party if need be. Again, precedents already exist in Canada. It would be in CN's and CP's interests to be part of that 'third party'. TTR could even be used (as it has in Vancouver) if the rail companies wanted to keep it close to being 'in-house'.
Then you'd still be waiting, and waiting for a long time. At least this way, they can upgrade the rest of the corridor in advance for when its needed.
The province is in a tight spot on this, damned if they do, damned if they don't. There's no clear answer on this yet, so logic dictates moving ahead on what you can do with a clear title to it, on the surmise that logic will rule at some point in the near future to allow completion of the whole. And that, for all the shortcomings of announcements and being played in the press, is what is happening. And I'm not one to defend this present regime's handling of transit, but on this one, they are hedging in a sensible way.