I never heard anyone using an excess valuation form on QR (or any other airlines).
All that QR mentions in conditions of carriage:
7.1 If in accordance with our regulations at some locations we offer an excess valuation facility, you may declare a value for Checked Baggage in excess of the applicable liability limits. If you make such a declaration you will pay any applicable charges.
I would assume Canada is not one of those locations. I would also assume that this is just a boiler plate and that there is no QR location where it applies (maybe USA).
Airlines apply the usual Montreal convention. Some countries have a specific law regarding maximum amount covered. The US has a maximum of $3,400, and US airlines routinely sell extra cover, but that is rare elsewhere (I don't know about Canada).
I strongly suggest that you forget about getting it from QR and get some additional insurance cover from a third party (maybe your credit card). Otherwise do what plunet suggested.