The USA international moved to the Stadium of Light from the Eredivisie side on Tuesday, putting pen to paper on a four-year deal.
Altidore spent two successful seasons with AZ, scoring 50 goals in 93 games including one in the KNVB Cup final win over PSV in May and he bolsters a forward line at the Premier League club that also features Danny Graham and Steven Fletcher.
Di Canio was quick to express his delight at clinching the 23-year-old's signature, and is thrilled with the firepower he now has at his disposal.
"I’m really pleased because a new arrival can benefit the squad and also individuals because there is competition up front," the Italian told the club's official website.
"Altidore is one of the top strikers in Europe. He only joined us on Tuesday but I’m very happy, curious and excited because I have a very good attacking side at the moment."
The 23-year-old's previous spell in England was an unsuccessful one as he was relegated at the end of a season-long loan deal with Hull City back in 2010.