England international Walcott scored a hat-trick against West Bromwich Albion on the final day of the Premier League season and keeps his place ahead of Frenchman Giroud.
Elsewhere, Wenger has made four changes to the side that beat the Baggies 4-1 six days ago.
In goal, Wojciech Szczesny resumes his role as cup keeper ahead of David Ospina, while further forward Laurent Koscielny, Nacho Monreal and Aaron Ramsey come in for Gabriel, Kieran Gibbs and Jack Wilshere.
Tim Sherwood, meanwhile, has also made four changes to his Aston Villa lineup.
Shay Given returns in goal, while in defence Alan Hutton and Jores Okore come in for Leandro Bacuna and Nathan Baker. Kieran Richardson returns at left-back, with Charles N'Zogbia moving into an advanced position to take Gabriel Agbonlahor's place.
Arsenal: Szczesny; Bellerin, Mertesacker, Koscielny, Monreal; Coquelin, Cazorla; Ramsey, Ozil, Alexis; Walcott
Subs: Ospina, Gibbs, Gabriel, Flamini, Wilshere, Oxlade-Chamberlain, Giroud
Villa: Given; Hutton, Vlaar, Okore, Richardson; Westwood, Delph, Cleverley; Grealish, N'Zogbia; Benteke
Subs: Guzan, Bacuna, Sinclair, Agbonlahor, Cole, Sanchez, Baker
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