Celtic skipper Scott Brown has led Gordon Strachan's national team recently but fit-again Fletcher is back playing at West Bromwich Albion.
"Scott has flourished under it when Darren's been injured," Wilson told BBC Radio Scotland.
"But Darren's more the leader of the country and has been for many years."
Wilson, who won his only international cap against Northern Ireland in 2011, added: "We're lucky that we've got two inspirational players in the middle of the park that can take that role.
"It is probably the biggest honour you can receive in football, so I think it matters a great deal, especially to the players involved - Scott and Darren.
"It will be of great importance to both of them, but I don't think either of them will be too disappointed or let it affect their game if they are not selected as captain."
Wednesday's friendly against Michael O'Neill's side at Hampden comes before Scotland's next Euro 2016 qualifier versus Gibraltar on Sunday.
"This game has been well selected by both sides," said Wilson, who now plays for Dumbarton after spells at Dundee United and Celtic.
"Quite often you can have these international friendlies that sort of peter out into nothing - a kind of drab affair.
"But with two competitive teams and players that have played against each other at the highest level in England and Scotland coming against each other, it gives it that extra bit of needle that you need."
Darren Fletcher's past experience leading Scotland could win him the captaincy against Northern Ireland, says former international Mark Wilson.