Fitting the CC-150T with a boom, re-modelling the FRS station and training/re-qualifying the FRS for boom AAR would involve substantial cost.
RCAF experience during OP SERVAL changed their earlier opinion of the Rafale; it was reliable, effective and flexible. It also refuels very quickly indeed, unlike the Typhoon.
See:
French Aircraft Manufacturers Say Rafale Fighter Can Provide Canada With Lower Long-Term Support Costs | Ottawa Citizen which is a reasonable summary, eh?