This isn't a silver bullet, but it will probably help. Say you are driving high right now. A cop pulls you over and suspects you are high. Now, he's got to get a blood test, which he needs to take you to a lab for and will probably need a warrant, because who is gonna consent to having their blood drawn. And most of the time, the blood test doesn't show anything useful, because unless it's done within a short time frame of you using cannabis, the THC will be broken down and it won't show that you smoked within the last few hours, only that you smoked recently, as in the last few days or weeks. So what kind of cop wants to deal with this? If you had an accurate test that could be done on the spot, it would be much easier for them. It's not like every cop will instantly be motivated, but I'm sure it'll help.

Glad to see someone else from Waterloo in the comments! I'm not sure that what local police department serves your area, but the Waterloo Regional Police Service are actually really ahead of the curve when it comes to drug impaired driving. They have more drug recognition experts per capital than almost any other jurisdiction in Canada and if I am remembering correctly they are making it mandatory to train new recruits in the standard field sobriety tests.

They should still be listening to your complaints, however. Hope you have better luck in the future.

Yes, it's WRPS for me. To be honest, I've kind of given up hope. Until the current chief is replaced there's just not much point advocating for anything.

Where is the correlation between these events and driving high being "totally a problem"

The correlation is that it's not clear that lack of a roadside cannibis test is the most pressing issue preventing cops from making our roads safer. There are dozens of things that could be better enforced (especially with more commitment to automation), but even "progressive" police departments consistently choose not to pursue most of them.