HI THERE ,
WRITING IN CAPS IS FUN. TO ANSWER YOUR QUESTION(in caps), YES WORKING AS APPRENTICE WOULD BE CONSIDERED UNDER CEC AS LONG AS IT IS A MINIMUM OF 30 HOURS OF 'PAID' WORK PER WEEK ON A PGWP AND UNDER NOC 0,A & B.
source: i called cic before on this issue and they seem to have no problem with that. neither have I read anywhere on their manuals and OP mentioning that it's not allowed. Only rule is that apprenticeship experience does not count while on a study permit.(but that's not in your case).
Edit: Again I might be wrong. wait for others to confirm