In the Canada Health Act, you could say a list of essential medicines would need to be determined by each province, and those essential medicines would be free at point of access, similar to what is currently a basic requirement of the Canada Health Act, so that there would be no cost barrier to accessing medicines that are important.
As to how the provinces decide what's in their basket, the Canada Health Act should demand that they be transparent and evidence-based about what they are going to put in. Then there's some sort of fair process Canadians can get their head around about what will be included and not included, so we're comparing apples and oranges. That would be a fine thing for hospital and physician services as well.
This would provide a lot of flexibility to the provinces. The federal government could offer, as they currently do, the potential to buy in bulk through federal auspices and then perhaps get a better Canadian deal. However, you don't have to be big to negotiate hard. My home country of New Zealand has four million people, and it's known for negotiating hard on prices with pharmaceutical companies. They have the lowest OECD prices in the world.