LAC (Library and Archives Canada) has just announced in their Blog that they have now uploaded the first batch of WWI CEF Service records to their website.
You can access these records at the LAC website, Soldiers of the First World War.
"As of today, 76,330 files are available online. Regular uploads of about 5,000 files will take place every two weeks. All digitized files are searchable by name, regimental number and rank. We will inform you as more digitized files are added to the database."