Giordano played one season of Junior A hockey with the Brampton Capitals of the Ontario Junior Hockey League in 2001–02 where he scored 24 goals in the playoffs to help lead the Capitals to the Ontario provincial championship. He then moved up to major junior, playing two seasons with the Owen Sound Attack of the Ontario Hockey League (OHL). He was the top scoring defenceman on the team for both years. As a 19-year-old rookie, Giordano recorded 48 points for Owen Sound in 2002–03 and, as one of the top first-year players in the league, was named to the OHL First All-Rookie Team.