Trade relations between the United States and the confederacy are an interesting area of speculation. Would the south have charged an import tariff on midwestern goods bound for New Orleans and overseas export? That would most likely have had the effect of spurring railroad growth to the eastern seaboard to bypass New Orleans, greatly diminishing port traffic there. Almost certainly they would have charged a tariff for goods imported from the US to confederate consumers, and southern goods entering the United States would have been subject to tariff as well.
We could look at what was happening when Spain held New Orleans for another possibility. States along the Ohio and Mississippi began talking of joining with Spain so that they would have access to New Orleans and the gulf. There’s a good book, “An Artist in Treason”, about a long forgotten Revolutionary War general, James Wilkinson, who was pretty much a double agent working for Spain in all of this when he was supposed to be our top general.
Depending upon how the Confederacy ran the New Orleans port the traders might have been content just to ship their goods there as they always had done. Or they might have been tempted to join the Confederacy which would certainly have been a recipe for political trouble. I kind of doubt that railroads would have been a practical solution because they are a very expensive alternative to using the rivers.