I tend to do all my merging via T-SQL as it's much more efficient (certainly for what I want to do)

There's a very good tutorial here (with all 4 SCD types)

http://www.sqlservercentral.com/articles/MERGE/73805/">

http://www.sqlservercentral.com/articles/MERGE/73805/

I'd recommend loading the Excel/csv data to some sort of staging SQL table

With the merge, make the source this staging table and the destination the final merged table

You can use an Execute SQL Task for the merge