I wrote that "By comparison, work on RER and LRT to YYZ is idling and uncertain." I am of course hopeful for YYZ's transportation plans, but I don't think anyone would deny that transit planning in the GTA and Ontario as a whole tend to be systematically swept up, and unfortunately out, with the winds of political change.
Other plans for YYZ are exciting, such as a high-speed rail link, but that HSR link is very much nascent at present, and is likely to be dropped entirely if the incumbent provincial party is replaced.
As for the REM vs the UPX, travel time to Gare Centrale on the REM will be 25 minutes on all-stops services, and 20 minutes on express services. The UPX offers service to Union in 22 minutes, which will increase with the new stop at Mt. Dennis. I think the quality of the REM is quite a bit higher than that of the UPX, due to the REM being electric and not diesel, there being 2 platforms on both termini of the REM, and all stations having platform screen doors, as well as direct connectivity to 3 metro lines. The UPX really should be electrified, regardless of the outcome of the RER mega-tender.