If boys’ schools had adopted a non cane policy in similar numbers as girls’ schools did, it may have shown boys, just as responsive to other forms of punishment similar to girls’ schools where the cane was absent. Co-ed schools using CP might have drawn on a positive comparison for boys, reducing number of canings for boys significantly in number to those received by girls.
I can recall no objections to the cane being for boys only when I was in high school.
Any objections voiced by boys would likely have been met with a caning for impertinence – or anything else the teacher could think up.
Boys were far naughtier and only they committed the offences that were punished by caning.