I believe that in Canada only a few careers require drug testing. Heavy Equipment Operators, Truckers, and I believe Law Enforcement jobs require drug testing beyond the initial hire test. And many regular jobs do not drug test upon hiring is my understanding. Until we can determine the last time someone used cannabis it will be a quagmire for employers. I suggest just keeping some fake urine around if you need it since most random drug tests are urine based and they don't supervise you while you urinate. Also consider trying to obtain a Marinol prescription if you can qualify for one. My understanding is there are a few labs that can tell the difference between natural THC found in Cannabis and synthetic lab created THC however it is extremely costly and employers do not frequently use them. With a Marinol prescription there will most likely be no way they can tell if you are using Cannabis recreationally unless you tell them or come to work under the influence.