It would still involve a large land grab, simply by virtue of both carriers wanting lots of tracks to themselves. What it would not be, in comparison the ALTO, is as much of a physical barrier, since the speeds would be slower and more level crossings would be possible.
Your proposal is closer to the original High Frequency Rail proposal, just on a different corridor. The key to fast (pick your speed) and consistently on-time passenger rail is separating it from freight. Somebody has to move. Europe can better get away with mixing non-HSR passenger rail and freight because they don't move anywhere near the tonnage we do in North America.
The speed a trainset is designed for or geared for isn't the defining issue; track classification rules are. Each class of track has a maximum speed for passenger and freight, and design rules in terms of curvature, grade, super elevation ('track banking'), maintenance standards, as well as crossing protection rules. The CN Kingston subdivision between Toronto (Pickering) and Dorval is considered Class 5 track and has a maximum passenger track speed of 100mph but not in all areas and further limited when switching tracks. The class of track required for high speed rail does not exist anywhere in Canada. In addition to very specific design parameters, level crossings are simply not allowed.