I think Imentioned to you that the Ontario death database at ancestry.com only goes to 1938 and neither William nor Rosa was listed.
I just found on the Archives of Ontario that they have deaths for 1938 and 1939. You need to look up the correct microfilm number and then they say you can find it at a Mormon family records library or you can order it through interlibrary loan.
The film numbers are
MS937 - 27 for 1938
MS937- 28 for 1939
so if you have a Mormon library near you thismay be the best way to try to find their death records.