Hello Luc,
Pleasure to be able to add a few snippets to unravel your family story, it seems a fascinating family to research and probably much more to uncover. The articles Shelly found for you were an excellent find to enhance your family story with pictures.
With regard to Harry La Montagne, I believe he was married before his marriage to Beatrice in 1906. Discovered another passport application 3 Jan 1899.
I Harry La Montagne apply for a Passport for myself and wife (unfortunately I cannot make out her name positively - its something like Emma

) She was born in New London. Canada 2 March 1871. He was born in New York 20 March 1868 and his father was a Naturalized Citizen. The application was made in December 1898.
From an article in
The Day - 12th July 1898The article refers to Mrs De La Montagne who was formerly Miss Emma
Morgan of Groton, visiting her Mother Mrs Thomas Morgan of Monument Street. Groton. Apparently she had been very upset by the death of her Father the previous year and had been in poor health. She took an overdose of morphine and although in a critical condition the prompt arrival of her Physician saved her life.
Since we know that Harry married Beatrice in 1906, it looks as if Emma La Mongne must have died between the Passport date in Dec 1898 and the new marraige in 1906.
http://www.rootschat.com/links/098n/