Building code for subways has changed since the first stage of Sheppard was prepared (tunnel diameter at very least). That stretch would need to be redone to a certain extent. Good chance materials requirements have also been changed (improved upon).
The EA itself may or may not be valid. Ford, would be unwise to use an old EA to accelerate a specific solution. He ran on a "listening to the public" campaign and as such is somewhat required to do a full Individual EA on Sheppard to decide what should be built. He can't claim to be listening to the public and not perform a lengthy public consultation.
Given the above, 2 years is optimistic.
I expect it will be March before a decision is made to cancel/continue the current project, June to negotiate with the province, +6 months for an EA (shortened process, could be much longer) + 3 years for engineering the new solution.
If a Sheppard subway is tendered during Fords first term I would be very, and pleasantly, surprised.