Size
The Labrador Retriever is larger: about 31 kg (68 lb) as an adult, against 20 kg (44 lb) for the Nova Scotia Duck Tolling Retriever.
Grooming
The Nova Scotia Duck Tolling Retriever needs more grooming, brushing a few times a week, where the Labrador Retriever needs a brush once a week.
Temperament
They differ most on affection (Labrador Retriever: a lap or leaning dog; Nova Scotia Duck Tolling Retriever: affectionate on its own terms) and on loyalty (Labrador Retriever: friendly with everyone; Nova Scotia Duck Tolling Retriever: bonded to its family).
Alike
Both are rated the same on independence: keen to work with you.