It just depends on which kennel club you're talking about.
The Nova Scotia Duck Tolling Retriever is classifed in the Sporting Group for the American Kennel Club and the Canadian Kennel Club.
It is designated in the Gundog Group by the Australian National Kennel Council, The Kennel Club, the New Zealand Kennel Club and the United Kennel Club,
In the Fédération Cynologique Internationale, the Toller is in Group 08 (Retrievers, Flushing Dogs and Water Dogs).