If you can't find a source for the brush in Canada, check out these guys:
They have the best prices in the US that I have found.
For 8x10 prints, you probably want a 2" brush. For 4x5 or 5x7, a 1.5" may be better, but I don't know, since I've never used one that small. You could do it with a 2", but you might be a little more precise with a smaller brush.
For 11x14, you might want to think about a 3", as it will spread out the chemicals faster than the 2".