by using data synchronization process..that means....
synchronization is the term used to describe the merging of
data from multiple data sources into a single block in a report

You can do a trick. Suppose u have different objects in  
two data providers (lets dpA and  dpB),dpA have product 
related objects for example product code, product name  and 
dpB have customer related objects.U drag a object from a 
dp, lets take dpA.Now when u try to drag a object from dpB 
u will not be able. 
For this , go to the tool bar->view data->definations-> 
link the object u want to drag(say customer name from dpB) 
with any object from dpA ->select Ok.Now u will be able to 
drag the customer name from dpB.  U will see that data 
displayed in the report is not correct.Now again go to view 
data and unlink the objects->select Ok.
Now u will get the correct data in the report.