From experience with my family................................
I had a similar situation.  I suspected that my great grandfather's surname in Europe was Susselovitch.  When he arrived in Montreal, he used the surname Saxe/Zaxe/Zaac from day one.  The was nothing in the Canadian records of him ever being a Susselovitch.  Then I found the ship manifest of his arrival in Montreal in the late 1880s, in which he is listed as Susselovitch.  That confirmed it.

Therefore, I suggest looking for the ship manifests for the Backmans in Montreal.  This can be a very painstaking task, because many - if not most - of those who emigrated to Montreal traveled on ships to some other North American seaport (for example: New York, Boston, St. John NB) and then continued overland to Montreal.  This, of course, was due mainly to the Canadian winter, when ships could not navigate the ice-covered St. Laurent River.
Good luck! :)
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Steve Goldberg
Jerusalem, Israel
Researching:
Sagan/Shagan family from Veliuona (Velon), Lithuania
Goldberg family from Vidukle, Lithuania
Susselovitch/Zuselovitch family from Raseiniai (Rassein), Lithuania