Do you think the North should build a canal across the Neck? It is the narrowest point in Westeros from one shore to the other. Also, the Fever River already covers some of this distance. Therefore, expanding this into a canal would allow travel from the Narrow Sea to the Sunset Sea. With the tolls from this and the increased trade it provided, the North could become quite wealthy. Engineering wise, it shouldn’t be as challenging as the Panama Canal as it would only cut through flat marshland.