Can an OC dictate that I use an electrician of their choosing?
No. They can only insist that you use a competent qualified electrician who has all the appropriate insurances. However, your strata manager might say there is a cost attached to confirming they are accredited so it might be easier and cheaper (for you) just to go with their guy. Sounds like a good case for getting competitive quotes.
Also, I’m not convinced the ceiling is common property if its suspended. Our strata scheme, desperate to cover its backside after it gave dubious permission for a ceiling’s removal, argues that the ceiling was, in fact, a horizontal, non-load-bearing wall and therefore could be removed without a by-law.
This is one of those cases where I would be tempted jut to get the work done and let the strata committee prove that you had done something wrong. Not that I’m recommending that … no, no, no. But if it was me …