The pair have both made their first-team debuts this season, but while Zaha has had less playing time, Januzaj is becoming a regular under manager David Moyes.
"They are both great players and have showed great character," Nani told the club's official website. "They both have good personalities as well.
"They have been given a chance to play in the first team and have impressed because they have lots of quality. It is normal for a young player to show good things when they have the right personality and mentality."
Zaha moved to the North-West club from Crystal Palace in the summer following an agreement made in January, while Januzaj recently signed a new long-term contract at United.