Different url to same page (with dynamic content)

I have a custom php script that in a specific page of my wordpress website is generating a dynamic content (ie. page mysite.com/citydetail that will load a list of places specific for that city).

The script is very simple, the source page (ie. mysite.com) has a link to mysite.com/citydetail passing some parameters (via POST form). The page retrieves the parameters and, after a query into my database, print the content page.

I would like to avoid to have the same page (ie. mysite.com/citydetail) with different content, in terms of SEO and google crawler probably is not the the best choice.. and I'm here to ask you the best way to proceed. I have permalink enabled.

I could do it adding parameter in the url like mysite.com/citydetail/?city=paris even if I'll not use that parameter (I pass the cityID via POST method).In this scenario I can have a list of different url containing the name of the city to which the contents page refer to. 

Do you see any negative aspect using this approach?Do you see valid alternatives I could use?

The main target is to avoid problem with my website and be sure my contents are properly indexed in google search.