The synchronization between iPad and iTunes gets started immediately after connecting the iPad to a computer installed with iTunes. In case if you do not want iTunes to start the automatic synchronization then you can change settings using the Preferences menu.
Launch iTunes then navigate to Edit menu.
Select Preferences from list of options available under Edit menu.
In the Preferences window, navigate to Devices tab then mark the checkbox with label as Prevent iPods, iPhones and iPads from syncing automatically. Click Ok button to confirm and save the changes. This would disable the auto synching of iPad with iTunes when the iPad is connected to computer and you will have do the synching manually.