Moyes was sacked on Tuesday after a disappointing first campaign at Old Trafford, and after Van Gaal was linked with a move to England, Roy has revealed that for former Ajax, Barcelona and Bayern Munich chief's management style would suit the Premier League.
The 44-year-old is quoted by The Mirror as saying: "He will never turn down Manchester United, believe me. I think that it's the job he really wants. And he will be a revelation at Manchester United.
"He is very disciplined, very strict and is very attacking in his philosophy. I know English football well, and his style is suited to that. He believes in wingers, he is very strong and very tactical. The best word that I can think of is demanding.
"On the pitch, every player will be told their job, they will know exactly what is expected of them, their position and role in the team."
Van Gaal is currently preparing to lead the Dutch national team at this summer's World Cup in Brazil.