Though Ford has green light the two extension, ML and IO will be responsible for the contracts as will awarded them and when. ML is holding everything close to their chest and tight lip these days on dates, timeframe, who is doing what and other info.
As to cost, will leave it to
@ShonTron since that is neck of the wood and haven't follow Brampton work that much, but the cost seems out of line for what has to be done for trackwork only.
As for design review, that is a different story depending on what stage of detail design was done when cost surface for the extension and where it is now. There is a big different been 30% and 100% design and only have to look at QQE to see it. Given there were a lot of changes after design reached 80% when construction was started only to see things ripped out at 100% on the surface section, More time is needed to get things right for 100% to do the tunnelling and building the underground.
I will leave it to the Brampton folks to provide more detail info, but the track recorder for the corridor are not great to say when the go ahead will happen and why I am using 2030-35 as the current timeframe for opening. The city doesn't what an extraction hole in the now so call downtown that is being torn down that it will have to be done sideway or the TBM bury under an area that will not require deep foundations down the road. In place of TBM, you can dig it out. The existing underground flood channel is to be remove to allow the redevelopment of the downtown area from what I been told and works in favour of of an side extraction of the TBM.