Peggy, the name is spelled "Scanlan" in 3 census records that I have seen.
Also, Patrick's age in 1880 is given as 47, making him born about 1833.Ellen is age 40, making her born about 1840.
The 1900 New Orleans census says Ellen emigrated in 1852. If that's true, she would only have been 12 years old and she and Patrick would have probably married in New Orleans. She is listed as widowed, and is running a boarding house.
In 1910 she is living with daughter Nora Blumenthal, a widow age 47, and Nora's 3 children, Joseph, Ida and William.Ellen is age 75.Says she had 8 children, with only 1 still living.
I know this is of no help in finding Patrick's parents, but thought you might not have this info.