I‘m not in the military yet but I‘m at the end of the application process. The CF is currently looking for people for technical NCM MOCs and Officers, particluarily CELEs. The trades that you don‘t see as "immediate vacancies" are still hiring but have attained a relatively suitable staffing level.
Don‘t worry about trades opening and closing. Its normal and what is closed at one point, will open again at some time in the future. Its as much as filling spaces as it is administrative
and course scheduling.
I was told by the recruiter that the CF considers all applications to the MOC and will chose the candidates much like a civie company. If your considering a MOC that opens/closes alot, or has an extensive a skill set (i.e. Comm Rsch: languages, computers,computer security, computer networking web design, record keeping; LCIS: electronics, communications, computer networking) it might be a thing to consider to take a few courses for familiarization if you don‘t already have a background. If anything, just something to put on a resume to make your profile look better.