Canada and Australia are basically the same, but in Canada there is a default understanding that most employers will help to sponsor an extended health/insurance plan.
I see no real issue with this, as it certainly does NOT mean they in any way control your options. As healthcare becomes increasingly expensive, the ability for employers to offer this benefit is degraded. None of that prevents you from doing what you want in terms of extra coverage though.
Most full time jobs that are also considered "careers" will offer some form of insurance benefits, and that usually includes health care. Aside from cost, the benefits of Group Insurance is that there are no pre-existing condition exceptions. You have guaranteed acceptance as a nature of your employment. This is a huge upside for people that aren't prefect medical specimens, and as a result employer offered extended coverage is significantly cheaper for the individual.
As I said you are starting to see changes mainly due to demographics and cost increases. The switch to Flex benefits, health spending accounts and such will see more "individualization" of health care costs in the future. Personally, I think HSA's are the best possible way to offer extended health benefits to employees, and I expect they will grow in popularity; analogous to what RRSP's have done to pension plans.
I find giving my employer power over my healthcare
You simply don't do this in Canada, although many people do have that impression. Example: Me. I have my government health care, my employer health care that I pay a portion of, and some extra private care that I elect to pay for.
