I'm a little surprised that Toronto's commuter operator doesn't have it's own topic (come to think of it, none of the Canadian commuter or mass transit rail systems have topics). So here's one.
Anyway, Metrolinx, the current owner of GO Transit, has bought some more of the GO Transit lines from CN:
There was a map of the lines which Metrolinx had already bought from CN in the last purchse announcement back in 2011:
This puts the great majority of the commuter rail trackage into the ownership of the commuter rail operator. The section from Oakville to Burlington will probably be purchased by Metrolinx sooner or later. The remaining part in CN and CP ownership is all part of freight mainlines and so probably won't be sold, at least not entirely. That remainder is the portion west of Burlington on the Lakeshore West line; the Doncaster diamonds and north of there on the Richmond Hill line, which is CN's transcontinental line; the portion of the Milton line west of the West Toronto Diamond, which is CP's mainline; and the portion of the Georgetown/Kitchener line west of 'Halwest' (between Bramalea and Malton), which is part of CN's east-west mainline through Toronto. That last section has had extra tracks added fairly recently.
The lines which don't run on the freight mainlines have also nearly all been grade-separated from them; the Snider diamond where the Barrie line crosses CN was finished most recently, while the West Toronto Diamond where the Georgetown line crosses CP is currently in progress. The Barrie line still crosses the CP mainline at grade, but there are also plans to grade-separate this. (The Richmond Hill line crosses the CN east-west mainline at grade before entering CN's transcontinental mainline and there are no plans to grade-separate this.)
Metrolinx/GO are also four-tracking the eastern part of the Georgetown line, including at the West Toronto Diamond, for the future Pearson Airport rail service, 'Air Rail Link', which will branch off the Georgetown line between Weston and Etobicoke North. This includes some trenching and station reconstruction at Weston. Plans also include major changes to Bloor station and linking it directly to Dundas West TTC station, and this seems to be partially funded.
GO Transit is also studying addition of service to Niagara Region. Among many other studies, this one seems likely to actually happen.
GO Transit, the City of Toronto, and the TTC, are also all currently performing large reconstruction and alteration projects on Union Station, coordinated with each other; there are honestly too many changes for me to keep track of them all. The pedestrian spaces in the station will be completely rearranged when they're finished, with changes to stairs, elevators, escalators, waiting rooms, passageways, etc. GO is also improving the track and switches and replacing the signalling, and renewing/extending the trainshed.
City's Union Station masterplan:
http://www.toronto.ca/union_station/rec ... proach.htm
TTC's Union subway station plan:
http://www.ttc.ca/About_the_TTC/Project ... Design.jsp
GO Transit's relatively uninformative Union Station projects page, complete with broken links: