The driving laws in Canada far as the road side stops to check for “drug use” I think could be argued in a court of law but I’m no lawyer- especially Canadian Law. I live in the states.
The problem is under the new law if a "drug recognition expert" rules that you are intoxicated, then the blood sample of >5ng results in confirmation that the tested substance is the result of said intoxication even though the blood sample alone is not proof of anything.
On top of that, this is even more problematic as the current evidence of the accuracy of the tests performed by drug recognition experts have shown that these tests are wrong >50% of the time. In other words, if a drug recognition expert deems you are intoxicated, even though if the test results in a positive it has a less than 1 out of 2 chance of being correct, since you consume cannabis regularly you will 100% be over the blood limit, and therefore are automatically guilty. Wow!
It has also been shown that one of the reasons for this accuracy is there is huge bias towards the drug recognition experts wanting to confirm with the arresting officer that said person is intoxicated due to pressure to not want to make their peer look bad (this is conscious and subconscious depending on the case)
The problem is that the only way you are not guilty is if you change the law, as under the current law, regardless of intoxication you are 100% guilty as the current law doesn't actually require you to be intoxicated to be guilty! Wow again!
I don't want to be the one to fight it in court ... at least they need "probable cause" to perform any testing for cannabis (no longer for alcohol, they can do this testing 100% randomly) ... so don't give them any probable cause (ie. store your cannabis in the trunk, wait an hour or two after consuming if possible, and definitely wait long enough that any acute effects are gone, get someone else to drive if at all possible, wash your hands and face before going anywhere after consuming, etc. etc.)
Basically medical cannabis users and cannabis users in general need to be 10x as cautious as they were when it was illegal, as now the penalties are much harsher, and the laws also provide much better tools for enforcement to law enforcement
... one example of the ridiculousness of the new laws and how much leeway it gives to enforcement is if an 18 year old goes to the "cannabis store" and buys a 1/4 of cannabis (or I guess 5 or 10g as it won't be sold in 1/8, 1/4, etc.), and then his 17 year old buddy gives him $10 for a gram, a cop can arrest him and he can be jailed for 14 years for this.