Had to be in Brampton last week and stop off at the Brampton Station to verify the info I have posted.
A retaining wall can be built on the north side of the corridor easy, but requires the use of an office parking lot at Queen St and the removal of a business across the street from it to do it. The retaining wall would run from Queen to the east side of the station along the edge of Nelson St beside the sidewalk.
The existing stairs and elevators will have to be remove unless making that platform very wide to maintain them. Still have to build a tunnel to get under the new track 1.
There is enough room to bend the new track cross Mills Rd to be on the south side of the fence on the west side of Mills and the driveway for the office building "IF" the boiler building, stairs and elevators are remove to maintain current width platforms. Will be a slow order with a big bend if these items are not removed. The only way to remove the slow order is to close off the driveway and removing the existing fencing. The lost of that driveway for the office building will have very little impact on it.
They have close the north stair off Main St, but no work is taking place, considering work to rebuild it had started sometime ago.
Otherwise, you can get the 3rd track in the current station area, but will see the lost of parking spots to do so. It will have an impact on the proposed LRT stop plan for this area, but better off leaving it on the street for the 2nd phase.
As for Weston Tunnel, that has been the plan going back to the summer time as well adding the 2nd track at West Toronto tunnel. Both have 2 tracks in them. Down side at Weston, only track 2 in place at this time as track 3 & 4 were removed for the rebuilding of the west platform. Would not take long to put in track 3 in, but 4 will go in after the platform is built.