No one knows what the outcome of this season UCL competition and which team will be the winner. I don't follow the bookies predictions before they have been wrong times without number. Actually, the big clubs like Real Madrid that you said is seen to be the favorite to win the competition but that doesn't mean that it will play out that way because football is full of surprises. Nobody expected PSG to win the Champions League last season and Chelsea to win PSG in the CWC finals.
Bookies obviously are not correct most of the times, I even think that they may not want to put up the correct team even if they have an actual idea of which team has got a better chance of winning the champions league this season and that is because it will count for them as loss which they will.not want to suffer much because they are in for profits. Real Madrid may be the favourite for many now but may end up loosing out in the champions league, PSG may surprise us and defend their tittle.