The humidity in Toronto in the summer can be quite oppressive, depending on which way the wind blows! That part of Canada is fairly flat, so boiling your brake fluid is not a likely issue. The rubber components in the system will allow moisture to get into the brake fluid. Now, given all of that, would three years be a major risk, probably not...but especially if you can do this yourself, why not do it at the manufacturer's recommended TIME interval.
Some things in a vehicle are distance related, some are time related...brake fluid is more time related so even if the car was not driven, but just sat somewhere, it would still be a good idea to change the fluid.
As I mentioned, there are brake fluid test strips you can buy that will give you an idea of the current state of your brake fluid. If after two years, it tests fine, yeah, extend it a bit.
2011 535i x-drive GT, 2014 i3 BEV