The issue is what compensation they get if VIA builds on their property. Their shareholders would justifiably hold management's feet to the fire to get every last penny, and their management are pretty aggressive about this in themselves. At a high level, CN and CP would be eager to take the money, but the parties could be a Billion $ or more apart on the price. Ask Bautista how that works ;-)
The issue with the Canadian is that CN quite deliberately ignores it, even though the schedule is heavily padded. Originally the schedule was set at CN's request with assurances that If VIA agreed to it, it would be achievable. CN simply doesn't care, and VIA is helpless to deal with the problem.
- Paul