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.
As expected, Arsenal should just defend their goals by avoiding conceding any goal from Real Madrid, if they can defend the game just as they defend their one goal against Manchester City in the first leg with red card that ended in a draw, I think they can be able to hold Real Madrid to a draw, or concede less goals, and I am very optimistic that Arsenal will also score goal in this second leg. Arsenal don’t heed to win this match to qualify, they can held them to a draw or score goals and avoid conceding more than two goals in the game.
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?
Arsenal can still be lucky to win Real Madrid, if it is possible then Arsenal has maintain their record of winning Real Madrid in the Champions League; but with all these rants in air from Real Madrid players and fans, I am expecting Madrid to win the game, but I don’t expect them to qualify to the semifinals.