The 1900 census shows John Gaven, born Nov 1838, widowed and immigrated in 1863, living in Allen Twp., Northampton County, PA.
The 1910 census shows a John Gaven 80, widowed, immigrated in 1848 living with his son William in Northampton Borough, Northampton County. Whether this is the same John is not certain. I could not find him in the 1920 census.
Honestly it may or may not be the same one, but it is worth looking into. His death certificate should have his parents' names. The obits and death certificates for at least one of his children should have Mary's maiden name.
The Marx Room at Easton Area Public Library has an excellent genealogical selection.
John was a naturalized citizen. The question is where did he file for naturalization. If in Northampton County it would have been at the Northampton County Prothonotary Office. These papers may have exactly when and where he arrived and where he was from.