Van der Sar, who turned 40 in October, confirmed this week he will quit at the end of the season after six years at United.
Going Dutch: Stekelenburg is top of United wishlist
And Rene Meulensteen, United's first team coach, revealed Sir Alex Ferguson has chosen ?10million-rated Stekelenburg, 28, ahead of Manuel Neuer, of Schalke, and Atletico Madrid's David de Gea after asking Van der Sar for his opinion on the 6ft 5in Ajax keeper.
'Stekelenburg is the keeper who is at the top of our wanted list,' Muelensteen told Dutch magazine Voetbal International. 'We talk a lot among ourselves about who should replace Van der Sar. Alex Ferguson has spoken about Stekelenburg with Edwin.'
Van der Sar will sit out today's FA Cup fourth-round tie at Southampton, leaving Ferguson to choose between recalling Tomasz Kuszczak or giving a debut to Anders Lindegaard.
But Lindegaard has been signed as a back-up keeper and Kuszczak will leave Old Trafford this summer. It is even possible Ferguson could sign a third keeper after assistant boss Mike Phelan confirmed United's interest in Rui Patricio, the 22-year-old from Sporting Lisbon.
'We've known Rui Patricio for a long time,' said Phelan. 'He's a young keeper with enormous potential.'
Ferguson paid tribute to Van der Sar yesterday, saying: 'When you get to the age of 40 and you're still playing top-level football, you know you're going to hit the wall sometime. All Edwin is doing is making sure he doesn't hit the wall while he's at United. If I was in his shoes, going out at the very top would be the thing to do.'
Thirty-something: Rejuvenated Dimitar Berbatov
Meanwhile, Ferguson has indicated that United will open negotiations over a new deal for Dimitar Berbatov, whose ?100,000-a-week contract runs out in 18 months.
The Bulgaria striker is finally producing the form United hoped he would when he signed from Tottenham for ?30.75m two-and-a-half years ago.
Berbatov already has 20 goals this season and Ferguson believes the player's birthday tomorrow will not be his only 30th celebration of the season.
'He's playing with great confidence and could easily get to the 30-goal mark,' said the United boss.'
Ferguson will take a 'strong' squad to St Mary's as he looks to avoid a repeat of United's only defeat this season - a 4-0 Carling Cup loss at West Ham, where the manager felt his fringe players let him down. He will be without full backs Patrice Evra and Rafael.
United midfielder Park Ji-sung turns his back on national service after 100 capsReal Madrid fail in bid to sign United flop Diego Forlan from city rivals AtleticoWatford make loan move for Manchester United midfielder Danny Drinkwater
Explore more:People: Alex Ferguson, Tomasz Kuszczak, Mike Phelan, Dimitar Berbatov, Patrice Evra, Edwin Van Der Sar Places: Lisbon, Bulgaria