Metrolinx has been sufficiently beholden to its political masters that any recommendations it makes is questionable. The decisions included the money-losing UPX, and buying LRT trains from Bombardier.

A high-speed rail line between London and Montreal has to go through downtown Toronto to work, otherwise people may be spending too much time getting to the airport. Route it through Pearson, and it's goodbye UPX (OK, that money-loser should be scrapped and written off). Oh there are not enough passengers beyond London for a high-speed train, and the more obvious line is Toronto - Montreal, but that inconveniently would not need a stop in Toronto's west end.