Real Madrid has very good history when they played at home. They often did some magicals to comeback even when they were at the critical situation. That might be the reason why the are in favor to win the game. However, can't really take google as a good source to predict.
I meant Madrid is not in a good position and they went down 2 0 in term of aggregate. I'm guessing they will against the wall with 10 men + 1 goal keeper in the penalty box. It's such a hard situation for them to secure three goals without conceded a single goal.
The aggregate is 3-0.
The reason why Real Madrid have higher probability to win is Arsenal don't have to win, they can play defensive. If Real Madrid won 2 goals more than Arsenal, they just win the match, but they won't qualify for the next round.
Expecting Arsenal to win is hard because from my own opinion, Arsenal won because they're lucky. The two goals free kick by Rice is really beautiful, I won't deny it, but who can guarantee Arsenal will score again in free kick?