Using old cedar deck boards to do vertical facia - what to seal/stain with?

Hello,

I'm reskinning my ~16x35 deck with Timber Teck and redoing railing to make it maintenance free.  Previous the front and sides had painted lattice which I'm also getting rid of.  I've stripped the deck and saved many of the cedar deck boards and used to replace lattice.  I've flipped the boards over and will sand them to get rid of the marks where they crossed the joists.  What should I seal/stain them with?  I prefer the natural look of wood but that may not necessarily go with the Mocha TT fascia (deck will be pictured framed and split with mocha, using pecan on the interior of the frame with Mocha fascia) so could be open to stain as well.

thanks for the input!