the part of the Gulf of St. Lawrence that separates Prince Edward Island from New Brunswick and Nova Scotia, in SE Canada. ab. 200 mi. (320 km) long; 9–30 mi. (15–48 km) wide.
North·um·ber·land Strait (nôr-thŭm'bər-lənd) An arm of the Gulf of St. Lawrence separating Prince Edward Island from New Brunswick and Nova Scotia in southeast Canada.