Available online at Library and Archives Canada: Veterans Death Cards: First World War.
Here is the card for Charles Alexander Sullivan, son of James Edward Sullivan and Anna (“Annie”) Moran:
And here is the card for Patrick Alfred Finner, son of Benjamin Finner and Mary Galligan:
The collection does not include those who died overseas in active service during World War I (for WWI combat deaths, try searching the database at the Commonwealth War Graves Commission), and it only includes those war veterans whose deaths were reported to Veterans Affairs. The LAC has a Search Help page for Veterans Death Cards: First World War, which explains how to search and how to interpret the abbreviations.