Wisniewski started his junior ice hockey career with the Plymouth Whalers of the Ontario Hockey League (OHL) in 2000. He improved every year significantly, and was drafted in the fifth round, 156th overall, by the Chicago Blackhawks in 2002. At the start of the 2003–04 season, he was named captain of the Whalers. That year, he scored 17 goals, 11 on the power-play. He finished 24th in overall scoring with 70 points, third amongst defensemen and just six points short of the OHL lead, set by Kingston Frontenacs defenseman Bryan Rodney. For his efforts, Wisniewski was awarded the OHL's 2004 Max Kaminsky Trophy as the most outstanding defenseman. He also took home the OHL's parent league, the Canadian Hockey League (CHL)'s, Defenseman of the Year award. This recognition gained Wisniewski a contract with Chicago, and a jump to the American Hockey League (AHL)'s Norfolk Admirals, the Blackhawks' top minor league affiliate.