Alexander, who has been in excellent form this season for Billy Davies' Championship promotion-chasers, has missed the last fortnight with a hamstring injury.
But he has been selected by national coach Walter Smith for the game at Hampden Park on Wednesday March 1.
He played for the Iron between 1990 and 1995, making over 160 appearances. He then joined Luton Town for £100,000 before making the switch to Preston in 1999.
He has made 21 international appearances for Scotland.