How to find out the content differences between 2 SQL tables and produce sync SQL
Other than tablediff and powershell mentioned in the previous answers, you can also use SQL with the UNION ALL statement to find the records that don’t match in 2 identical tables: 

SELECT MIN(TableName) AS TableName
   ,ID
   ,NAME
   ,lastname
   ,Address
   ,City
FROM (
SELECT 'Table A' AS TableName
    ,Customers.id
    ,Customers.NAME
    ,Customers.lastname
    ,Customers.Address
    ,Customers.City
FROM Customers

UNION ALL

SELECT 'Table B' AS TableName
    ,CustomersOld.id
    ,CustomersOld.NAME
    ,CustomersOld.lastname
    ,CustomersOld.Address
    ,CustomersOld.City
FROM CustomersOld
) tmp
GROUP BY ID
   ,NAME
   ,lastname
   ,Address
   ,City
HAVING COUNT(*) = 1
ORDER BY id;


Another option you can try is using Data Compare in Visual Studio itself. It compares data in the source database and the target database and creates a synchronization script for the tables you’ve selected for synchronization.

And last, but not least, you can use SQL data comparison tool - ApexSQL Data Diff, to set all synchronization options, map the tables and columns with different names, create your own keys for comparison in the GUI. 
You can schedule it to run unattended and all you have to do is check SQL Server job history in the morning.
If you need more details regarding these options, I recommend reading this article: http://solutioncenter.apexsql.com/automatically-compare-and-synchronize-sql-server-data/