Yes, from the conditions stated it would seem you fulfill the:
French citizenship acquired automatically at age 18
condition listed below.
You should check if your mother still has her French passport.
If she was became a Canadian citizen, Nationalization papers was well.
these documents and birth certificates may be helpful
I haved added a link ...
The present day Citizenship Laws are based on the version of:
Gesetz vom 15. Mai 1935 (RGBl. I. S. 593)
Before that the German Nationality was based on the Citizenship of a Bundesstaat that was a member of the German Empire
similar in nature to European Union Citizenship today
Reichs- und Staatsangehörigkeitsgesetz vom 22. Juli 1913
§ 1. Deutscher ist,...
Based on the German Embassy information quoted further down, the chances are high that have not lost your German citizenship.
To determine this property, you must apply for a Staatsangehörigkeitsausweis, for which the details can be found here:
Feststellung der deutschen Staatsangehörigkeit (Staatsangehörigkeitsausweis)
Before you apply, please read ...