Don't need to have 12 car trains as service levels increases using electrification. You MP40's for 12 car train beyond electrification points as service levels will be less and until CN/CP allow electrification in their corridor.We don't need second hand equipment. What they need are real dual mode locomotives.
Would the Bombardier ALP-45DP be powerful enough to pull 12 car BI-level trainset to 90mph between stations?
Could Alstom make them?
6-8 car trains is all you need for high quality of service with some lines being as low as 4 cars.
Never saw more than 8 cars trains in Europe doing GO style service, Even some trains doing intercity style service had only 8 DD cars.
Until a true expansion timetable comes into effect, the old cab cars can fill end until replacement starts to show up as well what equipment will look like.
Expansion will be on going before electrification starts and will take time to do it.