I doubt it. I'm not familiar with Canadian Law, but in the USA items to be searched for have to be listed on a search warrent. Now, in the case of searching for a missing person, let's say they search your place, right? You keep your drugs(whatever they are), in a lockbox in your bedroom drawer. The Cops go onto the box, and find the drugs. NO WAY(in my opinion) will that ever hold up in court(although you'd probably still get arrested for it-of course), since there is obviously no way any missing person would be hiding in a fucking 6"X9" lockbox.
I'll give you another example. The search the cops perform on you even before you are arrested(lets say at a traffic stop, and they suspect you of being under the influence or something)is called a TERRY SEACH, which gets its' name from Terry vs. Ohio(I think) which is(was) a precident-setting case. These searches are, by law, designed for the safety of the officer, and are a simple pat-down search to determine if the person being restrained is carrying any type of object, weapon, or whatever, that might endanger the officer in question. There was a local case here about 10 years back, where a local cop found a crack rock in a cigarette pack while doing one of these searches. It made it to preliminary hearing ONLY, and the search was thrown out because it went OUTSIDE THE LIMITS of what would be reasonably construed as a weapons search. In closing, the Judge said, that there was obviosly not going to be a handgun, and knife, or pretty much anything that could harm the officer in ther pack of cigarettes. The officer took the search too far. I dunno, maybe that helps.