Primary Documents and Official Accounts:

G.W.L. Nicholson, Official History of the Canadian Army in the First World War: Canadian Expeditionary Force, 1914-1919. Ottawa: Queen’s Printer, 1964.
(Available online as a PDF.)
http://www.cmp-cpm.forces.gc.ca/dhh-dhp/his/oh-ho/detail-eng.asp?BfBookLang=1&BfId=22
 
            See Chapter 11: The Battles of the Somme, July-    
            November 1916.

Historians’ Perspectives:

Introductory articles available online:

Legion Magazine: Canadian Military History in Perspective Series
Fateful Decisions on the Somme: Army, Part 56
January 1, 2005 by Terry Copp
https://legionmagazine.com/en/2005/01/fateful-decisions-on-the-somme/
 
Legion Magazine: Canada & the Victoria Cross Series
Valour on the Somme: Part 5 of 18
September 1, 2004 by Arthur Bishop
https://legionmagazine.com/en/2004/09/valour-on-the-somme/
 

Internet Resources: 
 
Veterans Affairs Canada - Battles of the Somme and Beaumont-Hamel
http://www.veterans.gc.ca/eng/remembrance/history/first-world-war/somme-beaumont-hamel
 
Library and Archives Canada - We Were There – Claudius Corneloup (22nd French Canadian Battalion) Courcelette
(Exerpts from his book (in French), other info about Courcelette photos, paintings, maps.)
http://www.collectionscanada.gc.ca/firstworldwar/025005-2200-e.html
 
Oral Histories of the First World War: Veterans 1914-1918
(Contains several interviews with transcripts and photos.)
http://www.collectionscanada.gc.ca/first-world-war/interviews/025015-1400-e.html