[sonysnob]

CN's track work is specialized, so they'll have to tender their own rail installation contract separate from the road work. They have to separate construction contracts like that in order to ensure that the right construction company gets the work. If you try to do too much in one contract an owner can loose control of specialty items because those items get subbed out to a subcontractor.

Because the old railway will be covered by the new highway, the MTO won't start any highway construction until CN relinquishes control of their property. The MTO could conceivably issue an advance contract outside of CN's property, but I think that would have too many logistical problems for it to make sense to parse out the work that way.