You mentioned giving birth with doctors and health care you trust in the US vs in Canada. While I do not have experience in every state but as someone who had given birth in Canada to 4 and 2 in the US. I would take the Canadian health care vs the US health care regarding birth in a heart beat. Plus she lives in a great area for top level health care. In the US I felt like a number, I actually changed doctors because the other one was talking about scheduling my induction date before I was even pregnant. I hate to say it but she will have better care and more options in Canada for pain management, midwives if she wants and recovery. She will be lucky if she gets much care after the birth of the child and not completely ignored by the staff in the US. In a country that everyone wants to sue a doctor, they tend to want to control everything and that tends to lead to C-sections. Oh and the likeliness that she will get the same OB to deliver that she has had care from is pretty low. They rotate and she most likely will deliver with a doctor she has never met.
By the way I lived on a border town when I lived in Canada, the amount of USC having their babies and going to prenatal care was super high on the Canadian side. They said it was just better and not because of dual citizenship either.
I feel she wants you to be a bigger part of this and she may think it is better to drive back and forth to the US for OB care and delivery. Yes it is legal but the border can deny her entry at any point. OB's also do not have to take on a patient in the US they can refuse to see her. It would be better to keep all care in Canada and in the long run so much cheaper for you. Even if you traveled to every appointment.