Panama Canal Expansion: A Boon for East Coast Ports?
A wider, deeper Panama Canal will open in 2014, meaning that bigger cargo ships filled with more containers of consumer goods can move directly to the population centers of the East Coast instead of stopping on the West Coast and sending the goods across the country.
48+ feet of depth minimum. The problem you have is the beam/width of the river. To go to that depth without bulkheads installed, it will have to be wide to counter situations similar to a continental geosyncline. Minimum, it will need two transit lanes, clearance for 2 panamax+ size carriers to pass one another, and pilots who will have to "learn" the areas of transits. It will be very expensive. Many US Ports on the east coast are taking on very expensive projects to accommodate these larger vessels. For example, PANYNJ is looking to raise the Bayonne bridge so that these vessels can access Port Elizabeth and Newark. Savannah is having to raise the CSS Georgia so that the river can be dredged.
However, the contested sovereignty claims over the waters may complicate future shipping through the region: The Canadian government considers the Northwestern Passages part of Canadian Internal Waters, but the United States and various European countries maintain they are an international strait or transit passage, allowing free and unencumbered passage.
How deep would it have to be to make a river from the Atlantic to the Pacific with no locks?
The problem with the channel aren't the diffrent surface levels of the both oceans it connects. They just vary by about 25cm. The problem is the hard rock in that region that makes it nearly impossible to dig a channel with a depth of lets say 20m in the right height.
Impound any vessel that attempts to use the passage. Impose fees that make it commercially unattractive.
Have a look at the map of the passage(s). Do you really want a giant tanker/bulk carrier/container ship transiting through the passage? Even without ice the passage is extremely narrow and would pose serious safety and environmental issues. This risk alone is worth leaving the area the largely unexplored wilderness it currently is alone.