It's a larger problem than AC. In Canada, almost all the defined benefit pension plans are under water and for huge amounts for some like BBD and AC.
The modification approval from the government and OSFI have to be applicable to others plans. I have in mind that with the 5 years ago solution, despite incremental payments from 2008 to 2013, the problem had not been fixed.
I think that the 150 M$ AC proposition for 10 years is not acceptable. I see a two part solution with a minimum reimboursment and a variable part like a % of Free cash flow. This way the pension plan will have a part of eventual surplus.