Kanu stepped up after the spot-kick had been given for a shirt-pull, but Liverpool goalkeeper Jose Reina saved and the Premier League game at Fratton Park finished goalless.
The Nigerian had missed a penalty previously for the club - against Blackburn last year - and Redknapp admitted he wished Muntari had taken the responsibility.
He said: "I thought Muntari would smack it and I'm happy to see someone whack it, personally.
"Kanu's missed one before so I wasn't over confident - but he's done great for me, he's been fantastic. We rely on him, really."