.html plug- in and search engine concerns

I really need to find out how the search engines will react to the wordpress site compared to my old dreamweaver site. I am using and html plug in to add .html to the end of my urls so the urls will look identical to my old urls. After I duplicate all my urls in my new wordpress site I will delete my old site and upload the wordpress site to the root. My question is, If I have an old site with a url like http://www.landscapingcalgary.org/paving-stones.html and I create a url exactly like that in the new wordpress site and it shows up like that in the browser , and I copy and paste the same content, then would the search engine see it as any thing but the same page as before it was wordpress?

Some folks are warning me in a big way not to mess with urls in wordpress or try to hack them with the .html plug in.
here is a quote from another wordpress professional:
“simply changing the urls of the pages in wordpress is not something that i would recommend. the permalink structure of a wordpress site is quite different than that of a static site, and trying to mimic your static page urls is only going to give you headaches in the long run”

Is there a way to find a correct answer to this ? Again, my objective is to disrupt the current urls as little as possible and keep everything the same as the current pages are doing well for me right now and I don’t want to mess up my page rankings.

Thanks for your help