Juan Mata, Marcos Rojo and James Wilson all found the net as the Premier League side won the fourth round replay comfortably.
Next up for Manchester United is a trip to League One Preston North End and Van Gaal is confident of his side???s chances this year.
“We have a real chance now,” he said. “Why? Because we are the highest-qualified team in the FA Cup.”
“I am not a casino man. But of course I think the highest-qualified teams have more possibilities to win than lower-qualified teams
“Maybe people are betting on us. I am not allowed to (but) I give you a tip.”
United have not won the FA Cup for 11 years but it looks to be their best chance of silverware this season as they trail Chelsea by 10 points in the Premier League.
???For the club, the fans, the coach and my staff, we want to win a title this year and the biggest chance is the FA Cup,” Van Gaal said.
“For me, personally, I won always a title in my first year everywhere I worked.”
United survived an early scare against Cambridge as Tom Elliott hit the post when he was one-on-one with David de Gea inside the opening minute.
“If they had scored the first goal then it would be a very difficult game,” admitted Van Gaal, who also said he took Robin van Persie off early so he would be fit to face West Ham on Sunday. “But I am very pleased because it was 3-0 and we have a clean sheet and we are in the next round.”
While Cambridge’s cup dream is over, the run to the fourth round is expected to net them around ??1.5m and manager Richard Money said that will be important for the club.
“It means we can be safe and stable financially,” Money said. “We are not going to have a spending spree in the summer and have one massive effort to be promoted.
“We need to grow. We need a new stadium and a new training ground or new??facilities at the training ground. That is what the cup run will do for us.”