I think a 18th Century Panama Canal is out of the question, even if you used the Chagres River most of the way and 'just' dug a canal to Panama City, but would a road be possible/practical/useful?
I'm not just thinking if technologically a road across Panama (or somewhere else suitable in Central America) to link the Pacific and Atlantic but if it would serve a useful purpose? Is there enough trade to make it worthwhile and would it save enough time?
And, has anyone ever tried?