I am not trolling when I say that the UPX should just run catenary subway trains as there are a couple good reaons why I think they are better than an EMU.
First, I think UPX should not be part of GO but rather the TTC and hence having it as another subway line with subway cars makes it more easily recognisable for Torontonians and visitors. Remember this line serves Union and Pearson so if there is a single line in the whole system that should be more sensitive to visitors who are not familiar with the system, it's this one.
Second, this is not a commuter route in the classic sense of the word. This is an inner city route that will have many more stations than it does now once it's rolled into Smart Tracks. That will probably mean stations at Etobicoke North, Eglinton, St,Clair, Queen West, and Liberty Village. That's a lot more stations and unlike standard commuter rail where 90% of the passengers are going to Union, there will be a LOT more on/off traffic at each station.
That means that you have to have trains that are fast not only in speed but also in station dwell time. Sydney and Melbourne have taken different paths in this over the years. Both have similar suburban rail systems but Sydney runs exclusively double-decker and Melbourne single. Turns out Melbourne's trains are considerably faster because double-decker trains take too long to load/unload. Melbourne once ran some double decker trains but got rid of them and now Sydney is going to do the same.
What has also made Melbourne trains faster over the years has been their choice of single-level EMUs. The one's they are now buying look inside and out more like subway trains than EMUs. More and wider doors, more subway type seating and design, lighting, all full accessibility.
I think Toronto should use just subway catenary cars if the TTC runs it. If unfortunately GO runs it then they should be single - level EMUs that are very much more like subway cars in their designs. These should not be just regular electrified GO trains with one floor but more akin to Metro/subway style EMUs to reflect the fact that this line will have quite a few stations and due to this and having a lot of on/off users at each station, dwell times must be kept to a minimum,.