Imps chairman Steff Wright told BBC Lincolnshire: "Keith was a guy who put so much into football but didn't get as much out of the game as others.
"The feeling among many people was to organise what will be an old-fashioned testimonial for Keith's family."
Alexander's long-time assistant Gary Simpson will be in charge of the team of his former players while the all-star XI will be led by Barry Fry, who as Peterborough chairman appointed him as manager at London Road, and MK Dons boss Paul Ince.
Although no players have yet been confirmed for the game, Wright added: "Barry told me that everyone he'd spoken to about the match is enthusiastic and wants to get involved.
"That's the reaction we'd have expected because everyone we've spoken to had that same sentiment about Keith."
The match will be played at Sincil Bank on Monday, 3 May with kick-off at 1500 BST.
Source: BBC Sport
Source: BBC Sport