Why does my cantilever brake squeal *nearly* all the time
I have cantilever brakes on my bike so I know the feeling. They just seem much more likely to squeal than any other type of brakes I've owned.  In the spring I had a bit of squealing. I cleaned off the rim, readjusted everything (cables, toe-in, etc.), and sanded down the brake pads a bit and everything seemed to be pretty good.

I also think it's something to do with the temperature.  Ever since the temperature started to drop, my front brake (also cantilever) has been squealing a lot. Even during the summer the first few times I would use my brakes they would squeal, but once they warmed up they seemed to work fine. I wonder if anybody makes a special brake shoe using a different rubber for cold weather braking.