Although I would be very happy to be proven wrong I agree that it is not very likely that we will see Queen Camilla in a tiara for this event. I think the clue lies in the post in the programme leading up to the King's speech: I doubt the Queen would wear a tiara for the swearing in as a member of the King's Privy Council of Canada. Let's hope that there will at least be some glitter, be it in the form of a big sparkling necklace and / or a sparkling brooch (preferrably with the "and" rather than just the "or").