Three Canadian residents who are not yet citizens are suing to remove the oath to the Queen as a condition of becoming citizens. They say that forcing them to swear allegiance to the Crown infringes on their freedom of thought and speech. Their reasoning doesn't add up.
The current citizenship oath is remarkably unburdensome. Apart from allegiance to the Queen, it requires only that new citizens promise to be law-abiding and to fulfill the duties of citizenship, which aren't even specified.
Compare the American equivalent, which demands the renunciation of any previous allegiance to another country, the defence of the Constitution and laws of the U.S., and the bearing of arms on the country's behalf. It even ends with "so help me God."
Swearing allegiance to the Queen is an affirmation of the Canadian Constitution. The Queen is the head of state and the Crown embodies the constitutional order. Many Canadians want to change that state of affairs, and they have powerful arguments in their favour. But one part of the Constitution, the right to freedom of expression, cannot be deployed to invalidate another part. The oath is not an unconstitutional imposition.
No applicant for citizenship can pick and choose which parts of the Constitution they wish to accept. Many Canadians would like to change the distribution of legislative powers between the federal and provincial governments. Others favour the elimination of the notwithstanding clause. And so on. Free speech entitles you to advocate amending the Constitution or the law; it doesn't mean that you can refuse to recognize parts of either.
Swearing allegiance to Elizabeth II or her predecessors was good enough for parliamentarians such as René Lévesque, Lucien Bouchard and hundreds of other Quebec sovereigntists, not to mention republicans across the country. Canadians are always free to choose to change the oath, democratically. That's how the system – the system new citizens pledge allegiance to – works.