This is the engine recommended line, and the most popular line played by masters...
Engines don't understand openings and masters follow fashion. There's a reason many of them follow fashion, so that they can keep up with novelties and so forth. But the positional line against the Wing Gambit is either takes on b4 followed by d5 or just d5.
Note that poucin stopped answering.
Actually, it seems that the best continuation in Mengarini variation with 2...Nc6 is not 3. b4!? but 3. Nf3 or 3. Nc3. So, U just make the transition to the classical Open or Closed Sicilian. But IM poucin says that it makes no sense putting the thick cross on Mengarini variation.
"it seems," What makes u fell 3.Nf3 or 3.Nc3 is better than b4?
What would be the point to play 3.Nf3 or 3.Nc3 when u can play them at move 2 and then play something more useful than a3?
We cannot say that provoking Nc6 is an issue for black...
About the variation given by pfren, here is most of the analysis provided by Soloviov in his "Modern Anti Sicilian a3" :
I think Yigor u trust too much statistics and website's evaluations. What's the value of chessok's assesment?
About Soloviov's analysis, black has some improvments, but this is not so simple.
Against an early a3 I use it as a target ... e6, Qc7, a6, Nf6, b5, maybe Bb7 but try to play b4 at the right time. Not Nc6 because it might prefer d7.
Most Sicilian players don't use e6 a6 Qc7 lines and even if they did they would be unlikely to attack early. In the Sicilian I always prefer to attack early, before development is finished and then try to complete development in a way that counters white's build-up. The idea is to try to force white into conceding weaknesses, like maybe g3 so I'll try to set up a mating pattern on the light squares in the late middle game or maybe doubled pawns on the c file, when you can go into the ending a pawn down as black and you might be better.
An interesting line which partially accepts the gambit (takes one pawn, but not the other): e4 c5 a3 e6 b4 cxb (accepts) axb Nf6 (declines, instead of Bxb4) e5 Nd5 b5 d6. Which side do you prefer? Can white still carry out a strong attack?
An interesting line which partially accepts the gambit (takes one pawn, but not the other): e4 c5 a3 e6 b4 cxb (accepts) axb Nf6 (declines, instead of Bxb4) e5 Nd5 b5 d6. Which side do you prefer? Can white still carry out a strong attack?
I've never faced that line... everyone goes Bxb4 in that position
Black has to play ... d5. Recapture with the Q.