If you want to know what your chances are of being selected for any of those occupations, you'd have to submit an application and submit the new scored employment form (SEAF). After that, a Military Career Counsellor (MCC) should be able to give you some idea of how likely you are to be selected in any of the trades, if you are found eligible (medical fitness, reliability status, etc.).
I haven't worked in recruiting for a few years but Signals and NCS Eng were chronically undermanned, particularly as they required certain STEM degrees (those with BAs need not apply). If you have a computer science or computer eng degree, then you likely have good chances of being selected for any of these trades (again, recruiting staff can give you better info, no point getting speculation from strangers online).
If recruiting staff suggest you are competitive for all 3 trades, then it may be in your best interest to limit your selection to just one occupation to ensure that's the one you get. While CELE and Sigs officers may fill some of the same roles in Ottawa, much of the postings in their careers will normally be within the Air Force or Army, respectively, so it may be worthwhile looking at where those bases are located... ex. would you rather live in Edmonton or Cold Lake, Gagetown or Gander, Petawawa or Trenton, etc. NCS Eng is quite a bit different than the other two (plus Navy postings = Halifax or Victoria) but they still maintain comms equipment, along with weapons systems. Certain responsibilities such as network management may be handled by NWOs, however (I know NWOs who've specialized in Info Management and attended the CAF Network Ops Course alongside Sigs and CELE officers).