There is high demand for all RNs here in Ontario at least. Specific positions you should look at is whatever type of care setting you would enjoy working in. Emergency department, palliative/long term care, ortho/rehab, intensive care, family clinic, pediatrics, all can be vastly different work environments. You'll do rotations through most of those in school so you can try to get a better idea of what those are like and how your interests fit. There are many further specializations within nursing you can pursue for changes of scenery later in your career. IMO cardiac cath lab nurses are badasses; they have to wear lead armor to work. The only speciality I can imagine being difficult for a male would be maternity.

For preparatory courses, look at your college's prerequisites for the nursing and make sure you're eligible. Otherwise I'd consider re-taking a course or two maybe if your old high school/college marks are borderline - college admissions is fairly competitive. Biology, chemistry, math and English I think are core pre-requisites. Best of luck.

Also, you may consider paramedicine if you're interested in general healthcare beyond nursing. The college program is shorter, the pay is pretty much at parity with RNs (Ontario), the job can be similar at times and very different at others. Feel free to pm specific questions.