Queen Side Castling

What is the best opening for white if you know that your opponent will castle Queen Side? 

How would you know?

It completely depends on their other moves. You can't base a strategy on simply your opponent queenside castling, which you will never know anyway.

No player can guarantee that they will castle queenside every game. If someone tries to do it every game, as part of their strategy, then they will hit a wall eventually where they'll realize that it's impractical--costing them moves and compromising their position in many situations.

King's Indian Attack seems like it would punish a queenside castle pretty hard for white.

The reason I ask is a friend of mine I regularly play will ALWAYS castle queenside if he plays black.

Doubling their C-pawn would be a good idea.