Best approach to "merging" two huge tables that are nearly similar in an OLTP environment.

I have two tables that are on the order 600 million records each (eventually to be about 2 billion).  This is an OLTP system so one of the tables (call it "Table A") is a live table but is only read from and is update/loaded on a daily basis.  The other ("Table B") is a staging table that data is loaded into from some secondary source.  This will likely grow to about 2 billion records.  Every month we need to run a reconciliation process where we make sure Table A has all of the records contained in Table B.  This