Friends at FB have posted or sent me links to several facebook pages and albums devoted to photos, postcards, and images of Greece from the late 19th / early 20th century. Theodoros Metallinos has posted hundreds of fascinating images in these albums, and this photos page at Istoria Eiknographia (PERIODIKO) also displays hundreds of old photos.
Some great early photos of Corinth, the Isthmus, and Canal among them….
Construction of Corinth canal, 1882 (from this page)
Construction of canal, 1884 (from this page)
Construction of the canal, 1886, photograph of Αναστασίου Γαζιάδη
This one of the functioning canal from 1902 (from this page )
Canal, 1935 (from this page)
German on the Isthmus, 1943 (from this page)
Couldn’t find a tag for this one at the canal.
Corinth, 1922 (from this page)
Corinthian Matters 
Are there any accounts of the final moments, when they let the canal fill with water? Speeches and ceremony? How did they do it?
Richard, I suspect there’s a goldmine of sources. I’ve stumbled upon American papers that covered the excavation, and there is a book or dissertation in Greek on the modern history of the Corinth canal. I haven’t yet seen it but hope to look more into this in the next couple of months.