I don't think that Ronaldo tries his maximum efforts in order to win another Champions League. He has already 5 or 6 I have lost the count.
He just chose Juventus in order to spend some time in Italy and enjoy the sun.
It would be interesting though to see him winning the CL title, with another different team. He is going to break another record in his career.
Ronaldo is the ultimate pro, I dont think Ive ever seen such a motivated & dedicated player. Winning the CL is tough, there are so many good teams who are capable of winning it. Juve will be one of the favourites but you need a lot of luck to win it.