in case you haven't already found this sitehttp://www.rootsweb.ancestry.com/~canns/
You will find the different Gen Web sites there.
Lunenburg County and Queen's County Birth, Marriage and Death Records from Primary Sources has
Amanda Elizabeth Gardner, b. 22 Dec 1862 with what looks like a baptism 11 Feb 1863 with Welkin - Liverpool Servant as parent
Most of the church records are held at the Nova Scotia Archives. I am not sure what the procedure is to access them.
Did you find Henry under Henry While in 1901 (automated genealogy)
What has lead you to know that Amanda White and Overpass are the same person. I saw a couple of family trees on ancestry with this same info.
I may have found a lead on William White.
1901 Census/Nova Scotia/Shelburne and Queens/Milton
White, William, adopted son, b. March 1, 1889, age 12
Anthony, Fannie M., adopted daughter, b. Oct 5, 1896, age 4
1911/Nova Scotia/Shelburne and Queens/Milton East
White, J. William age 22, b. March 1889
Julia, wife, age 19
Myra N. , daughter age 1
I think this is mistranscribed as I found a son for William and Julia named Myron Artelle
They are on the same page as Frank, Letetia and Fannie Anthony
I didn't find a marriage for William and Julia but did find a birth for
Myron Artelle White
b. Milton, April 28, 1910
parents William White and Julia Elizabeth Moore
Myron Artel whilte
m. Annie Mildred Anthony
1 December 1932 Milton NS in Church of Christ
Anthony's were the witnesses
Milton Community Cemetery has
Artell M. White 1910 - 1972
Annie M. Wife 1914 - 1982
David (son) 1949 -1949
I am wondering if Amanda changed her name once again or else left the province with daughter Sarah. It is also possible that Sarah was also put into domestic service and took on the name of the family she lived with.
The Amanda Elizabeth White death that is at nova scotia genealogy has her birth as 1849 - wrong year but other dates are correct. Also she is listed as married not widowed. I couldn't make out who the informant was or the relationship. The funeral home was listed though so someone in a local genealogy group may have more info.
Just for info - Liverpool is a small community on the South Shore of Nova Scotia and Milton is a village close by. I would contact the library in Liverpool to see if they know of local resources that aren't available on line.
Sorry I couldn't be of more help. Do hope this is a lead for William.