Modify a Maps plug-in for Wordpress business directory

I need to build a search results page in a Wordpress business directory. The search results page will show three business locations (*never more than three*) on a Google (or other) map. I want the info boxes on all three map markers to open simultaneously on page load. The information boxes need to contain HTML from the Wordpress database.

Finding it very difficult to find a WordPress maps plug-in that will do this.