Seaway International Bridge, International bridge in Cornwall, Canada

The Seaway International Bridge connects Cornwall, Ontario with Akwesasne and Massena, New York through a dual-bridge system spanning the St. Lawrence River. The structure comprises two separate sections that facilitate traffic across the waterway between Canada and the United States.

The South Channel Bridge opened in 1958; the high-level North Channel span followed in 1962. The crossing was renamed the Three Nations Crossing in 2000, and a new low-level North Channel bridge opened on 24 January 2014, funded entirely by Canada at an estimated $75 million. The old high-level bridge was demolished in 2015.

In 2000 the crossing was named the Three Nations Crossing, honouring the Mohawk of Akwesasne, a federally recognized tribe in the United States and a First Nation in Canada. Their reserve extends across the international border and also across the Quebec–Ontario line, with most of the land in New York. The name reflects that the bridge links a self-governing nation to both countries.

Vehicles must queue in designated lanes for border inspection, which can take time depending on traffic. Travelers should have travel documents ready and prepare for possible delays, particularly during peak hours.

The crossing is sometimes called the Three Nations Crossing because it connects three distinct jurisdictions at a single point. This unusual arrangement creates a complex crossing with unique traffic arrangements compared to typical border crossings.