If I may, NORML Canada believes that the focus should be on impairment assessment training, instead of chemical detection, because right now the science does not support the levels of THC vis-à-vis the actual level of impairment. That would open up many possible legal challenges. Cannabis can be detected in the bloodstream up to 90 days after it's used. A level of cannabinoids detected in the system does not necessarily equate to a level of impairment. That would be, I think, a serious mistake and would definitely open up numerous legal challenges. Even in the past there have been cases of people accused of driving impaired with levels of cannabis who have successfully challenged those charges. Getting officers who have training in assessing impairment from cannabis and many other factors would be a much more productive policy for Canada.
On September 12th, 2017. See this statement in context.