A friend comments on my earlier post, in which I argued that the oath of allegiance to the Queen which would-be Canadian citizens are required to swear is unconstitutional:
The wording of the oath of allegiance found in the Citizenship Act flows directly from the preamble and various sections of the Constitution Act, 1867 which clearly established the Queen as the head of state and Canada being a nation under the Crown. One part of the constitution cannot (the Charter) cannot be used to attack an act that is clearly authorized by another part of the constitution. The courts used this reasoning to dismiss attacks on separate Catholic School boards before. On a more basic level, it’s inconceivable that an oath of allegiance to the constitutionally appointed head of state can be found to be unconstitutional. You might say that is a tautology.
With respect, I think this is wrong.
It is true, as my friend says, that one part of the constitution cannot be invoked to challenge another. So, for instance, the Supreme Court has held in New Brunswick Broadcasting Co. v. Nova Scotia (Speaker of the House of Assembly),  1 S.C.R. 319, that the Charter did not apply to an exercise of Parliamentary privilege, because privilege is itself a part of the constitution. For the same reason, as my friend points out, courts have rejected Charter-based challenges to Catholic schools. That example illustrates the precise ― and fairly narrow ― scope of this doctrine. Catholic schools are specifically protected by subs. 93(1) of the Constitution Act, 1867. Their existence is effectively made part of the constitution.
The oath of allegiance is not. The Crown is part of the constitution of course (it is the nominal holder of the executive power pursuant to s. 9 of the Constitution Act, 1867 and a constituent component of the legislative power, pursuant to s. 17). But the Constitution Act, 1867 nowhere mentions or even implies the existence of an oath of allegiance for new citizens. It does mention oaths to be taken by voters (ss. 41 and 84), Lieutenant-Governors (s. 61), and members of Parliament and provincial legislative assemblies (s. 128) ― but not new citizens, even though it specifically contemplates “naturalization” as a legislative power of Parliament (s. 91(25)). This suggests that the oath of allegiance is a mere creature of statute, and thus fully subject to the Charter.
As to my friend’s “more basic point,” it is similar to what the majority of the Federal Court of Appeal Roach v. Canada (Minister of State for Multiculturalism and Citizenship),  2 F.C. 406, seems to be saying:
Of course, the total consequences of the swearing or affirming of these twenty-four words (as opposed to their nominal burden) are not at all trivial. Not only are the consequences as a whole not contrary to the Constitution, but it would hardly be too much to say that they are the Constitution. They express a solemn intention to adhere to the symbolic keystone of the Canadian Constitution as it has been and is, thus pledging an acceptance of the whole of our Constitution and national life. The appellant can hardly be heard to complain that, in order to become a Canadian citizen, he has to express agreement with the fundamental structure of our country as it is.
But I do not think that the equation of the oath of allegiance to the Queen with the Crown and the constitution itself works. Not every country requires oaths of allegiance to the head of state as opposed to the state itself or its constitution. The United States do not require its citizens to swear allegiance to the president. Even a country with “a constitution similar in principle” to Canada, Australia, does not require new citizens to swear an oath of allegiance to the Queen. Now if Canada also required an oath to the constitution and somebody challenged it on the basis that the constitution is monarchical, the argument might have more strength. As it is though, I do not think that it succeeds.