Merge data from a SQL Server backup
For your case i would recommend dbForge Server Data Compare for SQL Server from Devart. It looks very similar to the Redgate SQL Data Compare mentioned by Moisés González.

It allows you to compare your database with the backup file directly or with a second database. 

It shows you the differences between the databases:


only in backup / source database
only in target database
diffent rows / fields


You can select the data to restore or generate scripts for inserting in your current database. 

I use this software for our customers to restore deleted rows and even a restore of 5 million rows and update of another 5 million rows have been done very quickly. It works very well and can execute also very large repair scripts (the largest one i have generated was about 10 gig).

There is a 30 day trial available which may fit your needs. So you can give it a try without any risk.