All information from Ancestry.ca unless otherwise states
Death
Mary Ann Cain, aged 69, b Toronto died 10 Nov 1907, lot 35, conc 14 Mills Tsp, d/o Hugh Cain, no mother given, died of stoppage of bowels/one week. Roman Catholic. Registration # 023451.
Whoever was the informant on her death rego gave their father, Hugh Cain, and not her father so that doesn't help anyone.
I did not find a death rego for Hugh but I think he is buried in Trout Creek. Headstone says Hugh Cain died 21 Nov 1894, aged 64.
1871 census they are living Barrie, Simcoe North with Thomas 5, Mary 4, John 2, Hugh 6/12 b Oct. They were likely married around 1865/66.
Registration didn't begin until 1869. I looked on the Druoin Collection Ontario RC marriages but I didn't see them.
1861 has 2 Hugh Cains - one in Barrie aged 24 b Ont and one in Sunnidale Simcoe County aged 23 b Ireland.
1861 census has a Mary Ann Colejan, 20 b Ont living with father John b Ireland and siblings in Tecumseth Simcoe County.
It could be a possible.
1851 census is not available for Simcoe County.
Mary Cain, d/o of Hugh Cain and Mary Ann Callaghan, b Barrie 17 July 1863, died 11 Feb 1925 at Port Loring.
I looked up all the children's births/marriages and deaths that are on Ancestry.ca hoping that the name Callaghan may show up someplace but no luck.
1891 census McConkey, Mills, Hardy, McKenzie, Ferrie Tsp, Parry Sound District
CAIN
Hugh, 51, b Ont, parents b Ireland
Mary Ann, 45, Ont, parents b Ireland
Thomas, 20
John, 22
Hugh, 20
Catharine, 19
Margaret, 16
Patrick, 15
Joseph, 13
Ann, 11
Michael, 9
Bridget, 7
Caroline, 4
Bridget Gilbert, 54, Ireland, lodger
Thomas Cain, 33
1901 census
CAIN
Hugh, 15 Oct 1871, 29, b Ontario, Roman Catholic
Mary Ann, mother, 5 Jan 1844, 57, Ont
John, brother, 10 March 1869, 32, Ont
Maggie Richards, sister, 23 Feb 1874, 27,
Joseph Cain, brother, 9 Aug 1879, 22
Michael ", brother, 26 June 1883, 18
Bridget ", 15 Sept 1885, 16
Carolin, 14 April 1887, 14
All born Ontario. All Roman Catholic.
Don't think this is going to help your search very much.