I was told by a cancer patient in the US, who is a Canadian citizen, that specialized equipment and certain tests are not available in the entire system, or months-long wait times.
Medical bankruptcy is the most common form of bankruptcy in the US. I would say that for the massive portion of the US that is un-insured, under-insured or faces bankruptcy in the event of a medical procedure that substantially any tests and equipment for them are not available.
Canada has some of the best cancer survival rates in the world, and is substantially identical to the US. [1]
Further the US tends to skew towards early detection without a commensurate increase in survival rates, which means 5-year numbers in the US are higher than elsewhere in the world but it does not necessarily translate to lower mortality.
Not all treatments are statistically useful. In the US you can get anything you can pay for, even if it costs a million dollars and hasn't been shown to have any beneficial effect. In a national system you make statistical decisions based on cost and effectiveness.
Every doctor in Canada providing covered medical services is in-network.