Earlier quoted context omitted.
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A liberal protesting organization would have used bicycles and would thus have been legal.
Blocking traffic is still blocking traffic, though. In Canada, the "notwithstanding clause" essentially means no rights are absolute. Intentionally blocking traffic on highways here is generally illegal, insofar as people have a lawful right to drive there normally; see e.g. https://mtplaw.com/legal-news/arrests-for-blocking-a-highway... - and generally there will be clear evidence that such blockages are intentional.
Also relevant: https://edmonton.ctvnews.ca/can-protesters-be-charged-for-bl... ; https://ccla.org/wp-content/uploads/2021/12/Know-Your-Rights... (PDF from the Canadian Civil Liberties Association).