TBF, Ontario (and most importantly, Toronto) are going through the biggest transit expansion in all of North America. For those unaware, I'll list some of the projects by transit agency:
TTC (Toronto local transit) has a new metro (the Ontario Line/eventually Line 3), and 2 new LRT/light-metro lines under construction
GO (region transit) is undergoing a huge expansion where they're increasing frequency and electrifying the lines, while also doing a bunch of smaller projects to decrease travel times and points of conflict
Mississauga/Brampton have the Hurontario LRT under construction (also owned by GO/Metrolinx, but local transit, so I separated it)
Hamilton's LRT is in planning
ION LRT in Waterloo is planning Stage 2
There are too many bike infrastructure projects to mention, and a lot of new urbanist developments.
At the same time, the provincial government also has a number of projects that are crazy car-centric, like Highway 413, so it's not all good.
Pretty much all public works projects go over budget. Pretty much all private private projects also go over budget. However, people only complain about public transit projects going over budget. There are some legitimate reasons for this, like lack of institutional knowledge, but I think people hyper-fixate on public transit while roads "just have to be built, whatever the cost."
That's not a project in progress, so I didn't include it. It's also in a completely different region than the GTA, while all those projects are in the GTHA (except maybe Waterloo).