Seal Island Bridge, Through arch highway bridge in Victoria County, Nova Scotia, Canada

Seal Island Bridge is a through-arch highway bridge carrying Highway 105 across the Great Bras d'Or channel between Boularderie Island and Cape Breton Island. Its green steel box truss comprises eight spans, including a 152.4 m centre arch, resting on tall reinforced concrete piers armoured with cut stone at the waterline. Part of the crossing runs on a causeway to the wooded Seal Island.

Construction began in 1960 as part of the Trans-Canada Highway project, and the bridge, officially the Great Bras d'Or Crossing, was completed in 1961 at a cost of $4,652,850. It replaced two ferry services across the Great Bras d'Or, one at New Campbellton–Big Bras d'Or and one at Big Harbour–Ross Ferry. To appease communities fearing lost links, the crossing was placed halfway between them, forcing a 180° switchback on Kelly's Mountain.

The bridge replaced two ferry routes, changing the traditional maritime transportation patterns of local communities and reshaping regional connectivity patterns.

The bridge undergoes regular inspection and maintenance to ensure it safely handles daily traffic. Drivers should be aware that strong winds can occasionally cause temporary closures for safety reasons.

In November 2016, a diagonal beam of the centre arch span failed from fatigue and cracked through completely, dropping the arch 38 mm. The 2001–2004 deck replacement used precast panels one lane at a time, and the project won the Lieutenant Governor's Award for Engineering Excellence on 20 April 2004.