Until recently there were no residential code requirements in Canada about the strength of stair railing, and still none in the residential part of National Building Code. There are requirements about the spacing of spindles -- no opening larger than 4 inches to keep a baby's head from passing through and potentially getting stuck. There are local requirements that vary about the height of the railing. But only the commercial building code has any requirements about the strength of spindles.
In Ontario there was a court case where a residential stair railings had been replaced with a privacy wall that was little more than a drywall barrier. Two young football players went through this barrier while wrestling during a party and one of them was seriously injured. The result of this court case was that Ontario suddenly required that the commercial part of the building code be applied to residential stair railings and barriers. That effectively outlawed the use of softwood spindles as there has never been any strength testing of these railings. Of course that threw residential designers into a spin. We are still in the developmental process of this issue and it looks like it will finally be evened out when code officials consider the strength of three spindles together, since noone can go through just one. The rest of the country is sitting back to see what happens in Ontario.