Trade within Canada affects productivity and welfare. By analyzing Canadian data, researchers found that reducing costs of inter-provincial trade can lead to significant gains in GDP and welfare. The study shows that lowering trade costs by 10% can result in a 0.9% increase in GDP, while eliminating these costs could lead to gains of 3-7%, equivalent to $50-$130 billion in real GDP. The research also highlights that liberalizing specific sectors can bring the largest gains in highly interconnected industries.