A vote last week by Toronto city council saw the Scarborough LRT project ditched in favour of a new Scarborough Subway scheme.
$85m had already been sunk into the proposed project, which would see the development of the Scarborough SRT line into a seven-stop LRT.
The project was originally part of a master agreement between Toronto and the province, however following the 24-20 vote the city council, the project has been repackaged as new three-stop Scarborough subway.
Firm details at this early stage are unclear, however according to sources the preliminary estimate of the cost of the subway option is $2.3bn, plus certain transitional costs related to continuing and later dismantling the SRT.
As to whether the project will be completed using a P3 option, Jamie Robinson, director at Ontario transportation agency Metrolinx, said: "A final decision on a P3 would be up to the Toronto Transit Commission, but we would encourage them to look at it as an option."