www.collectionscanada.gc.ca/databases/cef/index-e.htmlSoldiers of the First World War
Albert Attree
Reg. # 775601
b. Jan 24, 1871
88 Beaconsfield Ave, Toronto
next of kin - wife, Mrs. Lucy Attree
enlisted in Toronto Jan 1916
Albert J (John) Attree
Reg. # 9996
enlisted Sept. 1914 Valcartier, Quebec
You can view the attestation papers at the above site and using the reference information, you can order copies of the complete military files. There is a section on How to consult or order a copy. There are approximately 25 plus pages in each file such as pay documents, medical information, transfer to battalions which can give you information as to where the soldier actually served. The war diaries for most battalions are available at Library and Archives Canada. The files also give embarkation and debarkation info. The cost is well worth the information that you will receive.
It does appear that your initial request for information about Lucy has been answered though as she is given as nok on both her husband and sons attestation papers.
www.canada411.cais an online directory and only lists 26 names with some being in Ontario, others in BC and Nova Scotia. You could always take a chance and write a letter to a few of the names and see if you get a response.