the above link has a list of the burials in the Nairn Hill cemetery and Julius is listed as COLLVER (same as in Ontario cemetery finding aid)
COLLVER Julius P. age 69 -1894-1963
Margaret M. age 101 -1893 - 1995
I am assuming Margaret is his wife.
If you click on their names it takes you to a photo of the headstones which show
Julius P. Collver Sept. 28, 1894 - Nov. 26, 1963
Margaret M. Collver July 21, 1893 - April 23, 1995
So if you were thinking this Julius and the one you found in 1820 and 1839 were same fellow, they are not.
I found birth of above Julius.
Cook County, Illinois, Birth Certificates Index, 1871-1922 about Julius Parmell Collver Name: Julius Parmell Collver Birth Date: 28 Sep 1894 Birth Place: Chicago, Cook, Illinois Ethnicity: American Gender: Male Race: Black Father Name: Howard Collver Father's Age: 28 Mother Name: Kathryn Sarah Ponnay Collver Mother's Birth Place: Rockford, Illinois Mother's Age: 28 FHL Film Number: 1287964
and a second entry - interesting the first says Black and the second says White
Cook County, Illinois, Birth Certificates Index, 1871-1922 about Julius P Collver Name: Julius P Collver Birth Date: 28 Sep 1894 Birth Place: Chicago, Cook, Illinois Ethnicity: American Gender: Male Race: White Father Name: Howard Collver Father's Birth Place: Canada Father's Age: 28 Mother Name: Katharine S Penney Mother's Birth Place: United States FHL Film Number: 1287740
He is in 1900 census in IL with parents, 1910IL with mother and siblings and grandparents
1920 - Julius is in Manhattan Assenbly district 11, , NY listed as Julius P. Colllvin (as indexed_ image looks like Collver, he is a clerk in advertising and a lodger in a household full of lodgers.
1930 OH with wife Margaret born Canada, immigrated 1914, and son John, age 3 - John M. born NY
WW11 draft card dated 1942 he is in OH and mentions wife Margaret
If you google his name Julius P. Collver there are two patents under that name so he may have been an inventor. In 1930 he is listed as advertising, advertising agency so maybe he invented on the side ?
It seems likely that Julius and Margaret met and married in NY as he is there is 1920 and they had son John about 1927.
There are many Margarets in Manhattan in 1920 who were born in Canada about 1893 so without her maiden name hard to find.