Google has most of the GTA on 2018 imagery right now. A few areas are newer with 2019, specifically Pickering and parts of Mississauga, but it's mostly 2018.
Google's "standard" imagery is often quite old, they tend to update it every 3 years or so on average I would guess, however if you use Google Earth still, it has a "historic" imagery feature that lets you view some newer stuff, that just usually isn't as high quality. Usually you can get some newer stuff that way, but even that only has 2018 imagery for most of the GTA. They did catch some new imagery for the immediate downtown core this spring though that's available through that.