Sicilian
https://www.chess.com/explorer/ in V2
https://www.chess.com/explorer?moveList=&ply=0 in V3
It will answer your questions about what alternatives masters have tried in all the major openings.
Depends, are you looking for the theoretical answer or the practical answer?
Theoretically? Best is 1.e4 c5 2.d4 cxd4! 3.c3 dxc3!
Practically? Transpose to the c3-Sicilian. It's easy equality, and psychologically gets at White because now you are in a positional game, not the wild sacrificial attack that White wants. 1.e4 c5 2.d4 cxd4 3.c3 and now it depends on what you play against the c3-Sicilian. If you play 1.e4 c5 2.c3 d5, then play 3...d5. If you play 1.e4 c5 2.c3 Nf6, then play 3...Nf6. If you play some offbeat line against the c3-Sicilian, then this approach won't help you.