I have a feeling that less damage will be done to GO electrification than Ford did to Transit City.
Likely some rebrandings (RER? SmartTrack? Etc), some cancellations of elements (Hydrogen, etc), some changes (e.g. merging UPX/SmartTrack/RER as a "fix that boondoggle" move) but the vast majority of the $13.5bn initiative would seem to survive. Worse is a few-years delay rather than the 1990s-era butchering of GO.
Big Move already trojanhorsed a lot of dependancies if GO RER is fully cancelled:
-- Union station revitalization is a cat in the bag
Union Station mall will almost a ghost mall offpeak, almost as bad as Aura's mall; possibly full of failing stores due to insufficient traffic. Major GO expansion is badly needed to justify the Union revitialization.
-- Eglinton Crosstown LRT and York TTC subway extension is a cat in the bag
They all have very significant GO integration that assumes GO is a FRTN (15-min AD2W). It would be very difficult to sabotage the Crosstown LRT.
-- Several transit networks at at varying stages of progress at the moment, all of which depends on GO becoming a FRTN (15-min AD2W)
-- The studies have made GO RER practically ready to begin construction after election, so rebrandings are much easier ("Let's brand this or that to something new but is actually essentially the same"). Reuse the majority of the studies and proceed with construction.
Conservatives are somewhat more transit friendly now than they were a few decades ago, especially at least to rail-based transit systems (subways, GO, etc) and the reach of GO is bigger now than it was (more rural ontario served now thanks to GO extensions since 1990s) so conservative ridership of GO is bigger today than it was in the 1990s. Many conservative politicians commute on GO now, and this kind of buffers things a little more than the Harris days.
Major disruptions to plans? Yes. Mostly unmodified? Maybe. Rebrands? Probably (SmartTrack is simply political branding of slightly enhanced GO RER). Ford Transit City league treatment of GO RER? Almost certainly not. I don't think so; way too scandalous to go all the way there. Four or eight year line-item gentler postponements? Possibly.
Many timelines are easily bumpable, such as Kitchener AD2W and Bowmanville, but those also serve many rural commuters too, so some conservative candy was also built into GO RER to make it unlikely to receive more than only partial Harris-style treatment (weaker than what happened to Transit City) -- Lakeshore East extension hadn't even completed yet to get conservatives used to riding it (like many are now). But now many extensions are already operating and conservative territory reach is bigger than it was in the 1990s.