Conceivably it's forever but the possibilities include the constitution being amended, a further court review further down the road (this would be in decades if at all), Canada breaking up or being conquered and all previous existing rights, laws and agreements being revoked for whatever replaces it. Overall nothing lasts forever and that includes the current iteration of the human species. Once we are gone, it's all gone.
Ok, granted. Perhaps forever should be changed to most likely all of our lifetime and those of our kids and probably their kids, for as long as Canada exists or as long as there are salmon left to fish, whichever ends first barring some huge miracle.