Real Madrid need to score at least 3 goals, in order to have chances/hopes left for reaching the final in Wembley, London. With the support of the Santiago Bernabeu they will start attacking from the first minute. Goals should be present here and they should come in both nets. Despite that Dortmund defend as a unit and with lot of energy, they are still prone to making mistakes, meanwhile they are good creative and skillful on the counter-attack, so I can't see Real Madrid defense keeping a clean sheet.
IMO, both teams are able to score 2 goals each, personally I expect Real to win the game with something like 3:2 or 4:2.