I would say subsection 320.27(3). I would determine exactly what the intent is.
Personally, I would suggest combining the random and mandatory aspects of the testing. I don't think anyone will oppose roadblocks, or mandatory testing of everyone at roadblocks.
However, detection—that is, police officers, working alone or as a pair, stopping people and having them undergo a test without reasonable cause—might be the most problematic.
If the mandatory and random aspects are combined, a police force could order that, during, say, a certain week, a test will be imposed on every three arrests. In other words, a person will be tested every three times someone is arrested. Consequently, it would be documented. This way, there would be no concerns about the fact that a police officer had to exercise judgment.