Did the Canadian government subsidize the big banks? The problem with pricing liquidity

Nick Rowe had a good comment on the CCPA's recent allegation that Canada's big banks were subsidized by taxpayers. In the comments I pointed out the difficulty of determining whether a subsidy or penalty had been paid to the banks because we lack a way to properly price and therefore compare the provision of liquidity services.

In effect, a government program called the Insured Mortgage Purchase Program (IMPP) announced it would buy $125 billion worth of insured NHA-MBS from the banks. It eventually bought $69 billion worth. In an alternative world, the same result is arrived at when

NHA-MBS liquidity options are sold by private actors to holders of NHA-MBS. These options allow NHA-MBS holders to sell all MBS back to the option writer at any time at a liquidity-protected price (some favourable point in the bid-ask spread). In a liquidity crisis bid-ask spreads increase, so the value of these options would quickly rise. The CMHC/IMPP provided MBS holders with a liquidity option, but we'll never know if they required MBS holders to pay the market price for this option.

Hey Nick, am I making any sense here?