Callendar with from reservation database and user

Hello
I have problem how to merge user name from user database with callednar with data from reservation database. On page i wannt to choose from user list, a person and below show that person’s meeting calendar ( different database named reservation ).
Datasource should bee from reservation & user database.

I know that solution is that i can choose person → go to next page and send parameters ( name of user ) to page with callendar but im trying to put all in one page.
Do enyone have maybe idea to solve this?