Prince Charles was right to worry about the unintended consequences on the Succession to the Crown Bill, though perhaps not for the reasons he anticipated.
According to Australia's Anne Twomey today -- no slouch when it comes to Crown constitutional law -- if the Duke and Duchess of Cambridge have as their first born child a girl, followed by a boy, the girl would become the Queen of the United Kingdom and the boy would become the King of Canada. This is apparently because according to the Canadian constitution, UK legislation can no longer apply in relation to the Canadian Crown. Thus by merely assenting to British legislation on the royal succession, Canada is only giving its consent on who would eventually sit on the British throne, not the Canadian one.
Hence, all that the Canadian Bill appears to do is to agree to a change in the law of succession in relation to the British Crown that does not in any way affect, or purport to affect, the succession to the Crown of Canada. The consequence would be that if the eldest child of the Duke and Duchess of Cambridge was a girl and a later child was a boy, the girl would become Queen of the United Kingdom and the boy would become King of Canada (assuming that neither jurisdiction had become a republic by that time).
Even more strange is the fact that the Canadian Government contends that this Canadian Bill, assenting to the alteration in the law made by the UK Bill, would have the effect of changing succession to the Crown of Canada. This is despite the fact that the UK Bill does not purport to apply to Canada and that s 2 of the Canada Act 1982 (UK) expressly provides that UK legislation can no longer apply in relation to Canada.
The history of the Statute of Westminster and its application clearly shows that the proposed 2013 approach by the Canadian Parliament of simply assenting to the British Bill will not have the effect of applying the relevant change to the Crown of Canada.
Moreover, s 4 of the Statute of Westminster has now been repealed with respect to Canada (Constitution Act 1982 (Canada), s 53 and Schedule, item 17) and the United Kingdom can no longer legislate for Canada (Canada Act 1982, s 2). It is therefore extremely difficult to see how the UK changes to the rules of succession can apply with respect to the Canadian Crown and how the Succession to the Throne Act 2013 (Can) could achieve that outcome, unless Canada was to revert to its pre-patriation and pre-Statute of Westminster position of being subject to British laws of paramount force.
It is likely that the Canadian Government took the gamble of this approach in order to avoid the hassle of obtaining the agreement of the Provinces while banking upon the likelihood that no one would have the standing or motive to challenge it. Moreover, if the Duchess of Cambridge has a first-born son, it will avoid the problem of having a female monarch of the United Kingdom and a younger brother who becomes the monarch of Canada. Hence, the chances of getting by with such a constitutionally shoddy arrangement are reasonable.
Nonetheless, it shows a disappointing lack of understanding of the Crown and its divisible nature and a willingness on the part of Canadian politicians to sacrifice Canadian independence to avoid having to engage with the Provinces.