Any registered nurse can be hired on a birthing unit. However, when I was in school to become an RN, it was obvious that it was a floor that a lot of the nurses wanted to work on, and competition for jobs there was pretty tight. So if you had extra training, with special courses you took yourself relating to labour, delivery, and neonatal care, you'd have a real advantage, but of course, as with most things, if you know the right people, you could be hired to that floor without special training. Also, ongoing professional development is a requirement to maintain your license to practice. There are people who get by with the bare minimum, and people who are truly passionate about their job and want to learn to do it better.
Is a US/Canadian midwife the same as an Aus midwife? In Canada, a midwife practices independently, like an ob, but with low-risk clients. Our local practice, for instance, has 4 or 5 midwives who work in the office together. Each client is assigned a primary and secondary care midwife, who do all the prenatal care, and both will attend the delivery, whether at home or in hospital. If you deliver in hospital, the labour and delivery nurses will not be part of your care - just your midwives. Whether you choose an ob or a midwife, a home or a hospital birth, your care is totally covered by the provincial health care plan. It's pretty nice in that way!