When the Queen Subway was originally proposed in the 1940's and 1950's, it was to use light rail (or the streetcars they had available then). Just like North America's first subway in Boston. The Queen subway would have only gone from Trinity-Bellwoods Park to Logan Avenue, where the vehicles would have branched off. In the east, one branch would have continued along Queen Street East or Kingston Road, the other branch would have continued along Gerrard to the Luttrell loop on Danforth Avenue. In the west, one branch would have continued on Dundas Street West to the Runnymede loop, and the other continued on Queen Street East and eventually The Queensway and Lake Shore Blvd. to the Long Branch loop. Things turned out different, but remember that that Queen subway was to use light rail (using existing streetcars at the time). It is my feeling that the Queensway right-of-way was to have been part the Queen subway, and could be now, if the Roads Department will ever give its holy blessing to true transit priority traffic signals.
The Eglingon Crosstown LRT will be a subway (period). That subway will run from just west of Keele Street to around Don Mills Road. However, instead of ending at those end points, the light rail vehicles will eventually continue on the the Airport in the west and Kennedy Station in the east.
If the Eglinton line was to be heavy rail, it would not continued past Keele or Don Mills. With light rail, we still get a subway, but now, in addition, rapid transit beyond.