That's a good question, I can't recall that I've ever seen any information about that. But I'm guessing most servers are colocated in already existing data centers. This ain't exactly AWS or M$ but 99Stack still has more locations than both of them, so they can't have much physical servers in each individual location. 🤔
I also don't expect it to be any major difference between data centers in terms of PUE or hardware in general, everyone involved want to keep the costs down, and green energy as well as low energy usage tends to be cheaper nowadays. Canada seems like a good choice, tho most locations won't fall far behind.
On average I think cold countries are better because those tend to sell excess heat to neighboring buildings. So Canada, South Korea maybe... but also warm countries which tend to use plenty of solar and wind.
I was surprised to learn that Texas use plenty of wind these days and barely no oil or coal, tho during the power outages I'm sure everything was powered by diesel. 😉