A lot does depend on the individual midwife. My daughter was born in Hamilton, the midwife I got was excited about and loves waterbirths, but there are others who will refuse to do them. Certain specific things are contraindicated for midwifery (ie, "complicated" pregnancies or certain health issues like high blood pressure -- I just snuck in with that one), it has to be "normal". And there are specific guidelines for when transfer of care needs to happen. But anything that's not specifically spelled out is up to the particular comfort level and training/experience of the individual midwife.
Like, my midwife was comfortable with my request to not have antibiotics at the birth ... since I'd refused the group B strep test, giving IV antibiotics is "standard" but you can request not to do it. She told me though, that one of the other midwifes on my 'team' would absolutely not allow that... if she ended up attending my birth, it would be antibiotics straight away, no argument.
So do talk things over with your midwife. They should give you detailed information about the 'rules' for transfer of care, I had to sign a form as I recall, or at least she had to check off some boxes on a form, stating that we'd gone over all that stuff.
In our case, we had a home waterbirth planned and she was fine with all of my non-intervention preferences. She was fantastic. Then my blood pressure shot up. Midwives do have hospital privileges, but that's a transfer of care situation. She got me an appointment with an OB they trust to check things out, and she also filled me in on what was likely to happen, she was extremely sympathetic and supportive and reassured my fears.
I ended up needing a transfer of care, was admitted to the hospital for an induction. It was traumatic to me after my fervent hopes for the home waterbirth, but it was SEAMLESS. It was not difficult (red tape-wise), the OB was not offended that I was with a midwife or anything like that, or critical of my choices at all... they're used to the model.
There were SOME issues in the hospital, of course. The drs and nurses didn't want to let me deliver squatting... but I insisted. AND my midwife stayed with me -- though she was not the one 'in charge', she was part of the team and served a sort of doula role for me. This is an example of how the Ontario model really is wonderful -- even when I needed the transfer of care, I was able to keep the person who I had worked with all along, beside me. It really helped me be comfortable.
THEN, the instant that my daughter was born, the care transferred automatically straight back to the midwife! So even though my daughter was born in the hospital with an OB and a medical induction... my midwife did all my home visits and I went to her office for the post partum chechkups.
I really think it's a great model. Best of both worlds. The midwives can handle all the 'normal' situations, but when medical care IS needed, it's seamless and painless to transfer. It was surprisingly uncomplicated.