These Arns are a tough lot to find information on. My g-g-grandmother was Magdalena Arn who married James Frederick Brown in 1862 in Ontario, later moving to Argyle, Sanilac County, Michigan. There is a really interesting website that has "pioneer sketches" from the Norfolk area and includes a comment that Cornelius Arn had 4 sons - Cornelius, Ely, John, and Charles. If you are interested, I found it really interesting reading about life in their day and time.

http://the-burgers.rootsweb.com/introduction.html

I also checked and had pulled your Charles F. Arn as a probable son of Cornelius from the 1881 Ontario census, where he is living with Lucinda and several children (Watts E., Willemina S., Adell, and Charles Burt). You probably already have this reference, but I have to say that I'm sure we're talking the same family.