Hello,
These are the steps that you need to perform in order to achieve your goal:
Let's assume that you have SiteA-ListA(ID, Title)
SiteB-ListB(ID, Title, Field1) where Field1 is the crosssite lookup field where we save the value in the format Site;#List;#ID
On the ListB you need to create a new field of type Numeric that would save the ID part of the above format let's name it ID1 (you can do this wither creating a custom action using QWp or a work flow or an even receiver).
On the site A create a page PageA, drop a qListForm on it, set it to the ListA and DisplayItem mode
Then on the SiteB qListView on the LinkTo property you add http://../SiteA/PageA.aspx?ID=<%ID1%>
On this way when the users click on the crosssite lookup field will see the qListForm on page A displaying the data.
Please check our documentation regarding the qListView and qListForm and LinkTo.
If you have any questions please let me know.