Yes, that should work, as long as both the cards are of same model. Any 1070 Ti will work, it doesn't need to be another founders edition. But, make sure you have an SLI bridge, as you will need that. Also, why do you want to go SLI? These days it's not actually recommended.
You would be much better off buying a SINGLE powerful GPU instead. SLI is not worth the hassle.