We are not talking about LE investigating a specific case. If they ask the hotel to be on the lookout for a specific known criminal or a specific missing person that is one thing. To tell hotels to pry into the private lives of each and every of their clients, to spy on them just to collect evidence, that would be unacceptable. And the police have no leverage to do that because hotels will not be breaking any law themselves. They cannot force the hotels to take exceptional measures to identify potential clients.
I have had family members and friends in LE and they all told me that investigations usually started with complaints from citizens. Sometimes, it takes several complaints from many persons about a location or situation. Sometimes, the nature of the complaint is serious, and it only takes one complaint.
So, I think in this situation, in a hotel, it will take many complaints over a period of time from many guests staying at the hotel. Then LE would go in and monitor the situation.
That being said, I have read in a US newspaper or newspaper website of investigations by a police departments in areas where they are heavily against prostitution where the detectives would stay out in the parking lot and monitor who goes in and who goes out.
I remember one account in Massachusetts, which is supposedly very anti-prostitution in some areas, where LE would corner guys who were in the hotel for an hour or less. They would say to them, we know why you were in there. You were seeing a young woman who is a known prostitute. We have video of you going into her room. They were trying to get guys to confess. They read some their Miranda rights even though they really didn't have much on them. I imagine the smart ones kept quiet, asked for a lawyer, and the scared ones waived their rights and confessed. But who is to say they LE can't try to get confessions from guys that way?
Yes and even more so since the new law is very contentious and debatable. This is something they will have to enforce carefully. They can't just play cowboy like they sometime do in other countries, because this is a challenge waiting to happen and no one will want to be the cause of that.
You think the current government won't pass this law because there are challenges waiting for them? I don't think so. So why would they wait to enforce it? And how would they be careful? I am not sure what you mean by that. They are going to want to catch guys in the act. A guy going to a hotel room, or inviting girls to his hotel room, or picking a girl up on the street in C-36 terms in all the same. In fact, I would think they would want to catch a guy at a hotel as the same as the street to show they are not picking on any one type of prostitution.