I am also interested in this question. I understand the Grand Canal in China was built before this time period, but I wonder whether there were any special engineering challenges involved in Suez or Panama. that would have made building them impossible at that time.

I remember my college lecturer us that Nero attempted to dig a canal at the Isthmus at Corinth. Nero started the project sometime after 67AD using 6000 slaves captured from the Jewish wars, roughly 3.4 km of the 6km was dug when the project was cancelled due to either or a combination of Neros assassination and the cost of the project.