Sometimes it can be worth looking for other family, especially if unusual surnames enter the tree by marriage.
The households have been linked (1901, 1911) at automatedgenealogy (found on a google for "leach ross john"):
http://automatedgenealogy.com/uidlinks/LinkHouseholds01to11.jsp#topHe had sisters Cora/Coral L 1897/8 and Mable S 1900/1 (with parents Sarah Leach and Ernest W Leach). ... In 1911, they were in Oshawa, Ontario South district (Sarah, Earnst, Ross, Cora and Mable, all spelled that way).
Per marriage records at Anc'y (I don't pay for access, just used the free search), Mabel Sarrah Leach married Orval W B Howie in 1921 in Ontario county.
Canada411 has several Howies in Oshawa, one of whom is an "O" (a bit of an unusual initial), with another few in Whitby. It isn't the world's most common surname. Maybe someone somewhere has a tree with Orval Howie, for instance?
The children of Mabel Leach and Orval Howie would be first cousins of the children of Ross John Leach and Marion Victoria Seale.
Aha, googling for "howie orval":
http://news.ourontario.ca/oshawa/2423773/data?n=29Obituary 1967, contact info for Oshawa library. Buried in Oshawa Union Cemetery. (The Ross Leach marriage notice is listed there too, along with the 1932 and 1950 obituaries of the parents Ernest and Sarah.)
I'm assuming you are not just looking for obituaries / info for a tree, but actually want to find living family ...
If you do the search for "howie orval" you'll find a fair bit of info about him: Orvil Wilkie Brown Howie, worked at GM, etc. Reversing the names, we found that as a young man he accidentally shot himself in the head.
Someone at GenesReunited does have him in a tree there ... and he is in four trees at anc'y ... one of which is called Seale Family Tree. It seems odd that his wife Mabel Leach is shown there but with no parents, when the connection to the tree would be Marion Seale, one would think, who is in that tree along with RJ Leach. Of course, perhaps that tree is yours or someone's in your family.

Have you considered the one Leach shown in Sault Ste Marie at canada411??