The US has so many large natural waterways and so much coastal land that canals were largely unnecessary and only really dug where it would be beneficial to avoid detours and dangerous areas like rapids or shoals. Plus much of the early US economy (in the colonial era, at least) was focused on the export of exotic goods to Europe, so colonies that became major cities like NYC were often built at the mouth of a river where river barges could unload valuable goods like beaver pelts right next to boats getting ready to make their way across the Atlantic.

The Mississippi River, the second largest river in the US, is over 3,765 km long, stretching almost from Canada all the way to the Gulf of Mexico. Why build a canal when nature has already done the work for you?