About the canals. Given the limits of Westerosi technology it would be impossible to build the canals you proposed. Most canals of any great size weren’t built until the Industrial revolution, and even then they were incredibly expensive. The required money to build them would probably increase the debt to the point that even charging for them wouldn’t gain any money for the Iron Throne.

I don’t think they are impossible. Mander to Blackwater is 50 miles, Blue Fork to Ironman’s Bay is half that. Compare that to the Naviglio Grande, built between the 12th and 13th centuries, which is more than 30 miles long, or the Canal de Briere, built in the 17th century, which is 35 miles long, let alone the Canal de Midi, also built in the 17th century, which is 150 miles long. And those are just the European canals – the Grand Canal of China is over a thousand miles long, and that was built in the 7th century.