I’m curious about where the idea for a system of canals in your Westerosi economic development plans came from. The only IRL historical example of such a system that I can think of was in China, and that one kinda broke down in government corruption and general infrastructure decay after a thousand years or so. I guess I’m curious about how you would manage the upkeep of these canals, and also how you would counteract corruption in trading ports and port cities in general.

Great question!

You’re not the first person to bring this up, but no, the Grand Canal of China is not the only example of premodern canal-building as an economic development strategy, only the biggest and most extravagant example.

Indeed, the reason why I put canals at the center of my Economic Development plans is that canal-building was a quite common part of Early Modern European economic development, as the Commercial Revolution offered enormous advantages to European states that could move goods faster than their competitors:

• In France, canal-building was a major part of the economic policy of more than a few monarchs and finance ministers: you had the Briare Canal (35 miles long) built to link the Loire to the Seine, and most impressively you had the Canal des Deux Mers which connected the Atlantic to the Medittarnean (270 miles long). 
• In Germany, the Prussians were absolutely mad for canals, so you had a series of canals built by zarious Hohenzollerns to link the Elbe to the Oder to the Weser.
• Due to the nature of their geography, the Dutch and the Belgians were huge innovators in canals going back to the 13th century, building canals to protect their cities from armies and floods but also to encourage water-based commerce, and to connect Amsterdam to Haarlem, Haarlem to Leiden, and so on and so forth.
• While most English canals were built during the “canal mania” of the 18th and early 19th centuries, there are quite a few canals built during the Early Modern period (the Exeter Canal in 1566, the Oxford-Burcot improvements to the Thames between 1605-1635, the River Wey improvements in 1653, the Stamford Canal in 1670, etc.)

In general, I opted for canals because you can build them with existing technology (they mostly involve a lot of manual labor, and various forms of simple locks were well within the technological capacity of Medieval Europeans) which means that the plan doesn’t rely on the discovery of new technology, they have a broad economic impact across a wide area by reducing transportation costs and lowering the price of bulk goods, and because Westeros has a lot of major river systems that almost, but don’t quite, connect so that relatively short canals can have an outsized impact on travel.