The Governor General's pension is calculated under the terms of the Governor General's Act in section 6, I think. I don't have the explicit figures, but my understanding is that the calculation is based on one-third of the value of the Governor General's salary in 1967. Then it's indexed according to an indexation factor that is explicitly spelled out in another act. Essentially the adjustment is made so it keeps up with inflation.
On May 15th, 2012. See this statement in context.