They both ended up needing the surgery. When the sister in the US visited her doctor, and he noticed the condition, the first thing he asked was if she had eaten breakfast. If she hadn't, he could schedule the surgery for that day, otherwise he'd have to schedule it for the next morning.
When the sister in Canada had the same condition, her doctor scheduled the next available surgery, and prescribed bed rest until then. She could get out of bed to use the bathroom and bathe, but otherwise should be laying down until she had the surgery, because a small mishap could damage her spine and cause permanent paralysis. Despite the severe risk of injury and the extreme side effects of prolonged bed rest, it took six months to get the surgery. If she didn't have support of her family, she wouldn't have been able to afford waiting that long.
When a medical condition impacts your ability to work, traveling to the US to pay cash for the surgery may be cheaper than waiting. There's even an official Canadian web page with advice for traveling outside of Canada to get medical care (https://travel.gc.ca/travelling/health-safety/medical-care-o...) and it expressly lists bullet points of the benefits of doing so.