I recently read your economic development plan for the North. You mentioned you wouldn’t build a canal near Moat Cailin (I had to look up what was meant by this) because of the Ironborn and House Manderly. However, in regards to the Ironborn couldn’t you just put a chain (like the one Tyrion used at the Blackwater) at the mouth of the Fever River and establish a port town/city there to guard it? Also, if House Stark builds it wouldn’t they control who crosses it (ex. House Manderly)?

You could, but there are ways of breaking boom chains, etc. 

It’s true that having built something generally helps, but you also have to consider that in medieval politics, proximity is hugely important. White Harbor being right next to Moat Cailin would give it more day-to-day influence than Winterfell, which is 400+ miles away. 

Whereas having the Canal pass by less than 50 miles away from Winterfell (and through territory that Winterfell itself owns) gives me a lot more practical control as opposed to de jure control.