I don't usually reply to my own messages, but in case this jogs anyone's memory:
I have identified my great-great-grandfather. I found him in the 1870 U.S. Census, living in Oil Creek Township, PA. He was married to Julia, and their son was William.
I then found Julia and William in the 1870 U.S. Census living in Denison, Texas. Only Julia had remarried and was now named Julia Caniford (husband Thomas).
Julia was from New York, as were her parents, so it would interesting to learn her maiden name. I'm guessing Myers since her son was named William Myers Esler. But I have not been able to locate a Julia Myers who would match.
John gave his birthplace as Canada, so now I'll try to track him from there.
Any and all input appreciated if this rings any bells ...