Wigan qualified for the match at Wembley with their shock 1-0 win over Manchester City in May's FA Cup final, just days before they were relegated to the Championship after eight seasons in the top flight.
While an immediate return to the Premier League is the club's main priority, they are taking seriously the opportunity to claim another trophy.
"We've got off to a good start in the league and it's a chance to use that as a positive ahead of Sunday," defender James Perch told the club's website, referring to their 4-0 win over Barnsley last weekend.
"We want to take the way we played on Saturday into the game against Man United but we know it's going to be a tough one, which means we really do have to be at our best."
For Manchester United manager David Moyes, the occasion is a chance to make an immediate mark at his new club.
Whether forward Wayne Rooney will appear on Sunday remains to be seen, however.
He has been the subject of two bids from Chelsea, following reports he is unhappy at the club, and missed the team's pre-season draw against AIK in Stockholm on Tuesday with a shoulder injury.
Moyes said after Tuesday's match that he doubted Rooney would recover in time to face Wigan, but if he is fit he has no concerns about playing him.
United fans have shown plenty of interest in the fixture, with the club having sold 42,800 tickets by Wednesday, a figure expected to dwarf the Wigan support.
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- James Perch