Normal wood floor stains and sealers won't work very well with both exterior use and south facing exposure. A good product that I use for many different deck surfaces is Sikkens Cetol SRD and Sikkens Cetol Dek. The SRD is a semi-transparent and the DEK has lower amounts of pigment making it more translucent.
Both products will stand up well with a maintenance coat every 2-3 years. It is recommended that all sides and the cut ends be stained prior to installation, back painted. Plus, the first maintenance coat should be within a year, then every 2-3 years.
Test any finish that you choose on the T&G wood before buying.