I agree. Indeed, part of me wants to say that Her Majesty actually appears to look "more Canadian" (whatever that may mean) sans the diadem. Nevertheless, the photo used on the stamp in question does emphasise the regal dignity of our constitutional monarchy, and it raises the question: is it time for us to make new set of crown jewels for exclusive use in Canada? We do have "our own" (to use "republican" rhetoric) royal standards, after all, all of which are comparatively new (not "worn-out symbols of colonialism").
In some respects, the process has already begun. The mace used up in Nunavut is a good example of how "purely Canadian" symbolism can be intertwined with royal symbolism without looking tacky. Contrary to "republican" belief, we need not abandon royal symbolism in order to make it more appealing to Johnny Canuck. We can "Canadianize" it, as long as our efforts are dignified and build upon the rich traditions of which we inherited from France and the UK.