As other have mentioned, the shortage is primarily caused by staying at home (COVID pandemic). Now that folks are working from home, they're doing "multi-tasking" with work and whatever they want on their own PCs (porn, games, videos, etc.). With the extra time from not commuting to work and back, some folks are willing to try to build their own PCs or even upgrade their existing ones. Folks have more time than usual as a result from working from or staying at home. This is the case for myself, my colleagues and my friends. Other folks may be different, but this appears to be the driving factor in why GPUs are in high demand.
To answer your second question on what to do with your $1500 Canadian budget towards a new PC, most of these pre-built companies show various options to customize your build slightly.
As an example, I went to Dell/Alienware and picked the Aurora R10 AMD option.
https://www.dell.com/en-us/shop/cty/pdp/spd/alienware-aurora-r10-desktop?~ck=mnYou can see the various prices and options it comes with. If you start with the cheapest, you can also customize further. Click and try it out.
A few tips on the customization you want for gaming -
-go for at least Ryzen 5 or Intel i5
-go for at least 16GB RAM
-go for at least 500GB SSD storage to start and you can always expand later
-pick any of the latest generation GPUs that are in stock and within your budget
I think someone already linked you to a customized NZXT build which fits the criteria I listed above and within $1500 USD.