Yes, the Missing Link would be essentially provide better-than-coproduction-league benefits, and they could tolerate sharing direction-optimized trackage. Three tracks would be all that is needed for the combined service for years to come -- not four. The extra track would be for traffic surges/passing/operational flexibility.In case it has been overlooked, CN and CP have co-operated a number of times before:
From the IBI Report:
A double track railway provides much greater capacity than the
sum of two single lines and offers faster transit times.
It is a no-brainer for CP even if Missing Link benefits is smaller for CP than CN, there is still big benefits for CP too.