Embedded View selection using multiple value field

Hope someone can help me. I assume I need to use WebQueryOpen, and run an agent, but I am going round in circles and need to know if what I am attempting can be achieved.

Requirement is:

User Log on via browser

Navigates to ‘Sites Form’ in DB1 with Embedded View

User ‘Sites’ names retrieved from doc containing Multiple Value Field in directory DB2 using user name for lookup.

Need to display Embedded View showing User’s Sites only from docs in DB3 so that user can then view details of their sites.

Even if you cannot give me the code, just knowing the events, agents, properties and a run through the logic I need would be great.

Many thanks.

Mark