Charles Roach, a permanent resident of Canada, wants the courts to remove the Queen from the oath of Canadian Citizenship.
It's been a while since I took my own citizenship test, but I seem to remember that the Queen is Canada's head of state. So I really can't see how pledging allegiance to her, in that capacity, can be unconstitutional.
Once you're a Canadian citizen you have every right to believe in and argue for the abolition of the monarchy, however, you can't with any integrity want to become a Canadian and at the same time reject Canada's head of state. Take the oath first, and then work to make change if you wish, Mr. Roach. Otherwise you're just a hypocrite.