Well-considered but I'm afraid flawed:
1) A river is at its most efficient when left in its natural state, not "improved".
That includes flood-plains, but it's not the river's fault if we build on them then moan when our homes flood.
A case-study:
The "Somerset Levels" in SW England. These fens were drained from the 18C onwards by networks of artificial channels locally called "rines", to the natural rivers that discharge into the sea in the Bristol Channel. They still work to some extent, helped by pumping-stations, but silting ofg the rines and rivers over the years has brought back much of the flooding.
Then we hear calls to "dredge the rivers" as used to be done. Only.... what is being dredged? That has to be considered carefully, for waterways only just above high-tide sea-level or a lake surface. Clearing accumulated obstructions and narrowings will help flood-water to escape, but mere deepening of rivers and lakes can only create deeps. It will not affect the water's surface altitude.
2) Canals and aqueducts will only work down-hill from their highest feeder streams, but I agree they might provide water-supplies or flood-relief, if designed suitably.
There have been suggestions aired in Britain of using its still fairly extensive canal network - now used only by pleasure-craft - as a sort of "water grid" but I don't know if this has been investigated seriously.
Using canals for transport is feasible but only to a limited extent, and the vessels still need engines or perhaps battery-powered electric motors.
Historically, canals apart from major estuarine (e.g St. Lawrence Seaway), and marine (Panama, Suez, Corinth) routes, canals originally overtook horse-wagons for a lot of industrial transport in the 18C. In turn they were displaced by the railway (19C) then both to a large extent to the roads (20C). The railways have made some come-back for moving bulk and container goods, thanks to
capacity, changing transport practices and increasing speed. (Most of the old-style goods trains on British lines were limited to about 30mph. The modern ones run at over twice that; passenger trains typically from 70 to well over 100, mph.)
The pressures were speed, convenience, certainty - and pure economics.
Canals for commercial transport worked well in Britain (their birth-place) and some European countries, but were rare in the USA, and are unlikely to return as serious inland freight routes.
....
So sidestepping party politics, what might the USA do?
Transport: I think your best bet is massive investment in the railways. I know they do carry huge freight tonnages but you need modern, electrically-powered freight trains cruising at maybe 60mph and passenger-trains at maybe 120mph; on the present routes. The continent could certainly host "high-speed" lines like the French TGV but they are very costly, politically sensitive and you'd need consider likely trade. So up-rating and electrifying the existing main lines may be better - and don't forget lineside fences, and automatic gates on level-crossings!
Water: Aqueducts could be worth considering where the physical geography allows, provided they don't lose water by absorption and evaporation. Otherwise the only practical way to deliver water to homes and business at State or National area level would be a comprehensive pipeline network.
Flood-relief may need large overflow channels and better planning controls on developments; but simply modifying existing rivers could even make things worse.
