Clue: Luxuriously happy state, Ontario, on the face of it; however, everyone's hammered on grass (4,2,3,3)
Answer: HIGH ON THE HOG
Explanation: Definition: Luxuriously
A charade of HIGH ('happy state') plus ONT ('Ontario') plus HEHOG, first letters ('on the face of it') of '**H**owever **E**veryone's **H**ammered **O**n **G**rass'. How 'bout that for a surface?