I like your sound economic development plans. Your canal proposals are a good idea. But I doubt you could do it. Large scale canal construction occured mostly during the industrial revolution and required a banking system, sufficient labor provided by the agricultural revolution and technology (dams, weirs, locks), which I don’t see in Westeros with all rivers in a natural state. Much depends on the distances and the terrain, but I think you are ahead of your time. So what is your take on this?

A couple things:

1. There’s actually quite a bit of large-scale canal-building prior to the Industrial Revolution. The Grand Canal in China is the longest canal in the world, and it was constructed beginning in the 5th century BCE, the Romans built dozens of canals complete with locks and dams and dikes, there are dozens of early modern canals in France and England that predate the industrial revolution, etc. 
2. A lot of the difficulty and cost of canal-building depends on whether they are ascending/descending canals or sea-level canals, so you can save a lot of time and effort and money if you can do the latter rather than the former. So rather than building the Mander-to-Blackwater Canal at Tumbleton, which would require building up Tumbler’s Falls, you do it further downstream on level ground and just build a level canal.