As a casual, you can make yourself available for one shift only, but you usually won't manage to make full time hours. When I first started working, I could only do days due to family obligations. There were times when I had two days work for a paycheque. I wound up working at five different sites to make ends meet and pay off that student loan. As new hire casual, you will be at the bottom of the to call list.
You have to be aware that COVID has caused all sorts of economic problems. Alberta nurses are facing cutbacks in numbers, benefits, and wages. Ontario is probably looking the same.