Professor Ryder is suggesting an option for sure, and it would require the legislative changes he described. I assume touching the Canada Health Act is politically very hard, so people would rather avoid it. This is part of the reason I suggest you could achieve exactly the same thing through a series of contracts. Provinces that wished to could enter into a contract with the federal government to have a formulary based on their relations under this contract and to take steps X, Y, and Z to negotiate prices on behalf of all of them. To make that powerful, they would each agree not to strike separate deals with pharmaceutical companies, so they could not be divided and conquered.
If contractually the provinces band together such that none of them can split and purchase medicines separately, you have just created a system in which the maximum bargaining power exists. Whatever supplier wins a negotiation will supply all the provinces. They get the biggest economy of scale, so they can afford to bring their price down the deepest, and it can be done without legislation.