WORKING IN CANADA- DRUGS TEST??

Hi all,
I have a question but i dont even know if this is the right place to post it.
Soon i have to go to canada for work. I have to start at an industrial plant calld XXXXXX. I got an invitation where it says that a part of the safety training is taking a drugtest for cannabis, cocaine etc. I'm from holland and we dont have this kind of tests for cannabis, because you know cannabis is allowed to get consumed in holland in your private space.
I was reading an article about a court that allows XXXXXX to use random drugtests since 2014 weblink removed

So my question is: Are people here on from canada who ever workd at XXXXX or a industrial plant simmulair to XXXXX. And i want confirmation if it is realy random for everyone or that workers from abroad have to take it mandatory. If its not random its better for me to stay in holland and avoid the costs and the bad name. I think its a bullshit test because THC stays like 4 weeks in your blood and a company can just refuse me working because i had a joint 4 weeks ago in amsterdam.

This isnt' really an immigration question is it.

If the company (details of name and weblink removed) does random testing, then it likely applies to all employees.