The john sweeps in Canada have focused on street prostitution and are primarily motivated by complaints of residents from neighborhoods where the activity takes place.
Not because of the supposedly "higher" moral purpose of the prostitution laws (which, according to MacKay, is exactly what C-36 is all about), a notion around which there is no social consensus. SPVM, in Montreal, have made it quite clear that it's not something they're interested in pursuing, and there other LE agencies which have similar policies (Victoria, Vancouver, for instance).
And when stings have been used, they have been done in instances where at least one of the following was occurring: underage sex workers, actual trafficking, and coerced prostitution.
As for the States, where both sides of the equation are illegal, prostitution is in the bottom tier in terms of arrests. Not only that, but the rates of arrests related to prostitution have been in decline over the past 20 years; see Figure 8 on page 4, here:
http://www.bjs.gov/content/pub/pdf/aus9010.pdf
Outside of specific circumstances, there is less and less interest in going after the simple client.