As far as I'm concerned, random breath testing is a significant constitutional violation. The current Immediate Roadside Prohibition system in British Columbia comes as close to random breath testing as I think will ever pass constitutional muster. Currently, police have the power to make a demand for a breath sample pursuant to the Criminal Code, but so long as the breath sample is provided, the driver has no recourse to challenge the validity of the demand. Refusing carries the same penalty as blowing a "Fail", and unlike just blowing a "Fail" on an ASD, a refusal is also a criminal offence. Which means, effectively, that police are empowered to obtain breath samples from an individual at random, and there is no recourse so long as the driver provides samples.
Worse than that is the suggestion that random breath testing at large is a reasonable proposition. It completely disregards the Charter. And while there is a significant amount of carnage caused by impaired driving incidents, that does not mean that suspected impaired drivers do not deserve Charter protection.
The only way that I can ever settle the idea of random breath testing against constitutional rights is if the results of the breath tests are used only for the immediate removal of drivers from the road for 24 hours. With no notation on the driving record, no vehicle impoundment, and no fines or penalties. Then the public safety objective achieved by the liberty and privacy intrusion does not cause any imbalance.
The difficulty with this method appears to be that it puts an end to the criminal prosecution of drivers, where random breath tests are used. There would have to be some mechanism to distinguish the impaired drivers warranting criminal investigation and prosecution from those who should only be removed from the road on the basis of a suspicion. In British Columbia, this has resulted in very few impaired driving cases being charged and prosecuted. The time and effort needed to investigate an impaired driving case criminally is much greater than the ease of the roadside system. And although IRPs were never supposed to be issued in cases where there were accidents or injuries, that has not been the realistic outcome of IRP investigations in BC, thus far.
It seems that there is really no truly viable alternative to the method established in the Criminal Code to prosecute and investigate impaired drivers. But random breath testing with punitive or criminal consequences is absolutely no way to fix any perceived defects in the system.