Wow. That is a contentious and fun piece of history right there. From what I remember reading, you both are kinda right, but I believe some of the details are a bit off.
For what its worth, I had to pick up a book off the shelf to check myself.
The Canadians were the first in 1914 to implement "trench raiding" that would later evolve into battlefield tactics that would resemble what would be defined as "stormtrooper tactics" or "specialized assault infantry tactics".
These tactics are characterized by integrated supporting arms, decentralized command and control, engagements in dispersed patterns, squad-based fire and maneuver, and demanding independent initiative and leadership from the small unit commanders down to the NCO level. Standard stuff these days, but combined arms tactics was revolutionary in the period between 1890's-1920's.
So perhaps the Canadians "implemented" it first in 1914-1915 during the beginnings of the trench raiding.
The difference between the Germans and the Canadians is that the Canadians kinda stumbled into it organically on the field, while the Germans concurrently "discovered it" built it from the ground up and formed specialized units dedicated to it. By 1915 Sturm Battalion Rohr was formed, and within a short period every German division was working towards integrating strum troops. Their training and tactics influenced by Major Reddemann and Lieutenant Colonel Rohr. Substantively, what the Germans were doing was institutional and would go on to influence militaries around the world. So the gap between "first use" and "discovery" is extremely narrow.
Put another way, the Canadians figured it how to do something without defining it and never developed it further, but the credit of discovery goes to the Germans, because they were not just using it "ad hoc" on the battlefield. The Germans understood it well enough to create a whole new doctrine to describe it, recognized its importance, and committed whole units and offensive operations around the doctrine.
Further, the Germans (
and a few other notable participants who were paying attention) retained and continued to develop and improve the doctrine after the war while the Canadians let the knowledge fade out of the ranks and it had to be relearned later.
But this is just me regurgitating information that you can read for yourself and I might be getting some of the details smudged.
Here are some notable books on the subject written by people who are far more qualified to weigh in on the subject. As it feels like this may be an issue of pride, I included historians that were Canadian military officers in the list of books below.
"Stormtrooper Tactics: Innovation in the German Army, 1914-1918" by Bruce Gudundsson
"Doctrine and Dogma: German and British Infantry Tactics in the First World War" by Martin Samuels
"A Lesson in Success: The Calonne Trench Raid, 17 January 1917." by Andrew B. Godefroy
"Toward Combined Arms Warfare: A Survey of 20th Century Tactics, Doctrine, and Organization" by Jonathan M. House
“Men against Fire: The Doctrine of the Offensive in 1914” by Michael Howard
Of course all of this ignores that the Germans were observing the start of similar tactics being used in the Russo-Japanese War of 1904-1905.