Why not just call CBSA and ask them?
As suggested, for a definitive answer, contact CBSA, or just go do it . . . . let us know how it turns out . . . .
Interpretation can depend on punctuation. Time is awasting, surely your best course is asking the Canadian authorities for the ruling/clarification you think worth seeking. And post the result.
So I called the CBSA this morning and spoke with a very pleasant and helpful agent about the wording and intent of the ArriveCAN reporting requirements for foreign national boaters who anchor in Canadian waters, but do not come ashore, or moor or come alongside another boat in Canadian waters. She listened intently, put me on hold twice to ask a supervisor for clarification, asked me a few follow up questions. While not in writing, it's as clear as Canada can make it. And while Trawler Forum membership affords us little or no authority when it comes to border issues, it is rewarding to see that virtually everyone here was right about their interpretation of the rule.
In addition to landing on Canadian soil, mooring to a structure connected to Canadian soil, or coming along side another boat in Canadian water, anchoring in Canadian water also requires the boater to use the ArriveCAN system. And as Soo pointed out, for me, until the rules change, it ultimately would come down to vaccine status. If you are not "vaccinated," you can not anchor in Canadian water.
https://www.cbsa-asfc.gc.ca/travel-voyage/pb-pp-eng.html
For what it's worth, the very pleasant and helpful agent also wrestled with the wording and had to seek an interpretation from her supervisor twice. I was grateful that she was not dismissive and went to lengths to clarify the wording.
In the end, perhaps I should have posted this question at an English grammar forum rather than a boating forum. And yes, Benthic, punctuation does matter.