If he leads Real to another CL win scoring doubles and triples in the semis and the final, surely he must be in contention for the best player of the CL, period, not just as a goalscorer. It would be his fifth victory, which is very impressive, especially considering his stats in the knock-out phase. I hate to say it but you can't avoid the evidence. Up until 2015 I would have argued on behalf of Messi, but CR has really turned it around since then.
On the other hand, for example, Messi is indisputably the best player ever to play in Spain, where by comparison CR has not been nearly as decisive.