Copy or Move Data from one Database to other Database and have one more destination option

Question

Let's say I have 2 databases:

1. Source database we will call SRC
2. Target Database we will call TRG

SRC has about 300 tables that are in TRG as well (same schema and same table names). There are other tables in both databases as well which are different (but we do not care about it).

Right now there is Truncate Load solution (through SSIS) which is running everyday for about 300 tables (300+ GB data).

But I want to change it to incremental load, where we want to use Redgate SQL Compare tool where we compare SRC to TRG and update TRG (this sounds simple), but we want to compare SRC snapshot to TRG snapshot in Redgate Tool and then move data to TRG itself.

One other twist to add to it, also want to store SRC somewhere either in SQL Server database or CSV or in any other form (please suggest), from where this data we will move to Azure database.

One other scenario if possible, perform comparison of SRC with SQL Server database or CSV or in any other form through Redgate SQL Compare tool, and then update TRG, and then truncate SQL Server database or CSV or in any other form through Redgate SQL Compare tool and load SRC.

Please suggest which is the best way, or any other option much better than this.

Hope I have explained properly.