Canals are smaller, though I grant there may be a canal which is longer than the shortest rivers.
Still, I haven't seen proposals for canals which would be comparable to the Mississippi or the Amazon.
A quick Google, and...
The Grand Canal (also known as the Beijing-Hangzhou Grand Canal) ... is the longest canal or artificial river in the world ... linking the Yellow River and Yangtze River. The oldest parts of the canal date back to the 5th century BC, although the various sections were finally combined during the Sui dynasty (581–618 AD). The total length of the Grand Canal is 1,776 km (1,104 mi).
I am also not sure why you think the technology is difficult. You just dig. The traditional "technology" is slave labour.
This thread is intended to provide a space for 'crazy' ideas. Ideas that spontaneously come to mind (and feel great), ideas you long wanted to tell but never found the place and time for and also for ideas you think should be obvious and simple - but nobody ever mentions them.
This thread itself is such an idea. Or rather the tangent of such an idea which I post below as a seed for this thread.
Rules for this thread:
If this should become a regular thread I suggest the following :