I assume that the point made by @smallspy was that capacity is constrained enough to not rip out any second or third tracks the second we have HFR along the Havelock Sub (as @crs1026 keeps insisting for whatever reason), but doesn’t cause enough pain to justify (yet) the expense of restoring a second track along the Eastern half of the York Sub. CN’s focus would therefore be to maintain the current capacity along its Toronto-Montreal main corridor and to mitigate the impact of the single-track section between Doncaster and Pickering…Silly question.
I see they have (badly decayed) second track still in place for a good distance around Zoo Road in Rouge Park, if that area is a bottleneck, why is the second track in dis-use/storage track condition?. (I'm not questioning your statement, I'm curious about CN's thinking)
I see most of that section (12 miles York Sub) either had a second track at one point or is set up for it (bridges that allow for two tracks)