I do not think so, Cambridge is the tougher board, in pretty much all cases except biology.
In mathematics, there is simple and further. It depends on what you choose.
Just remember these courses are optimised for what it required, so if ur son does not plan to study FP in A levels, then dont do it. I have always supported Cambridge because it brings out the most creative. But Edexcel is for the average guy, in my perspective.