Biosimilars instead of biologics? Why not?

So, what's with all this talk of biologics and biosimilars recently?
Biologics have been around for a while now. They are a type of drug or medication made of living cells that are injected or infused into patients by IV. They are typically used for chronic conditions like rheumatoid arthritis, Crohn's disease, ulcerative colitis, diabetes and to increase the white blood count of patients receiving chemotherapy treatments. And they are expensive. For example, one popular treatment for rheumatoid arthritis costs almost $1,000 per vial.
Biosimilars are near-copies of original biologic drugs whose patents have expired, making them much cheaper than the equivalent biologics. They are perfectly safe, having passed all the same tests as biologics, and in the vast majority of cases they will do the same job as the biologics they replace.
The reason these drugs are in the news is that Alberta (yes, Alberta again) is in the process of passing a law to replace biologics with the much cheaper biosimilars, in cases where patients are on government-sponsored drug plans (i.e. not covered by private insurance, and not patients who pay their own drugs out-of-pocket). Pregnant women and children are also excluded from the law. The province says it expects to save between $227 million and $380 million over four years (a huge spread, which suggests they don't really know), money that can be applied elsewhere in provincial healthcare. British Columbia and several European countries already have very similar laws.
This sounds pretty sensible at first blush, but some specialists in the affected medical fields are crying foul, saying that some patients will be adversely affected. The bulk of the  international evidence, though, suggests that biosimilars are just as effective as the biologics they mimic, and the Alberta plan does include a provision that a patient can apply for an exemption if their doctor can prove that there is a medical reason why switching would be inadvisable.
It seems to me that the law has thought of most possible drawbacks and made provision for them. So, much as I hate to offer support to an Alberta government that is getting so much so wrong, this is one case where it seems to be getting it right.
But another question I have is: what are these "government-sponsored drug plans"? Do Alberta and BC have some kind of provincial pharmacare system that I knew nothing about? If so, why doesn't Ontario?