All I know is that random drug screening has been ruled to be unconstitutional and an invasion of privacy here in Canada. You can test before hiring someone (ie. your oil workers getting tested before getting sent to a new job), or after an incident, but not randomly. I work in a safety-sensitive position and have had to navigate the testing protocols, so I would know. Contract workers and subcontractors are an exception (some truck drivers, oil workers, etc) in that whenever you take a new contract or job with a new client, you would be subject to their pre-employment drug screening. Companies cannot have their own policies which contradict or contravene employment laws or the Charter of Human Rights, this would be illegal.
There was a big push to try and allow for random drug-screening in the Alberta oil-sands to cut down on the rampant abuse of hard drugs and the like.....no way in hell the unions or human rights types will allow it and for good reason. No one in this country wants to see random drug testing anywhere as that would be a scary precedent for everyone, not just LP employees....it definitely would not be something to take glee in as all Canadians would eventually pay.
And why would LP employees be any different from pharmaceutical employees working with much more dangerous, valuable, and addictive drugs such as opiates? These employees are not screened, and there would a much greater chance of abuse in those cases. Doctors and nurses are not tested either, and they have constant access to controlled drugs. I'm not sure who your source is, but I'm calling B.S. on this one, nothing to see here.