Transport Canada has not established a standardized number. However, in regulations the department published, it lists the factors—such as the railway grade and the weight of the train—to take into account to determine the required number of handbrakes to activate. A combination of factors determine how many handbrakes are necessary. Before being updated, the regulations simply stated that a sufficient number of handbrakes should be used. Since then, the requirement has been standardized by establishing a chart relative to the grade and the weight, making it possible to determine the minimum number of required handbrakes.
On March 21st, 2016. See this statement in context.