The 27-year-old had parted company with the club at the end of last season after failing to agree a new deal. But he will join up with his Villa Park team-mates on their three-match tour of the United States after being named in manager Paul Lambert's 25-man squad.
Guzan joined Villa from Chivas in 2008 and has been second choice for the majority of his time at Villa Park. But he impressed while deputising for Shay Given when the Republic of Ireland international was injured last season, and Lambert expects the American to put pressure on Villa's number one.
"I've watched Brad and some of his games when he was in the team last year and he was excellent," Lambert told the club's official website.
"I know he's always had that stigma of being the number two behind some really good goalkeepers here. But when you come back at the start of the season nobody knows what's going to happen and it depends on whoever does well.
"Brad played very well the time he was in and maybe he found himself a bit unlucky to be back out. The club needs two or three good goalkeepers, so when Shay comes back from the Euros it will be a big bonus and we will see what happens."