What is the content of this? A disc? A code?

It is a playset piece for the console games and also includes a web code for the PC version.

My son has the ps3 marvel superhero 2.0 edition. can he play this toy box 3.0 edition on his machine ? because i'm confused with what comes in it? thx

You can play it on the PS3, BUT for all 3.0 pieces (figures, playsets, and this expansion) you need the 3.0 game software (the disc).What this is is basically another playset. It's a piece you put on the power base (like the Avengers Tower piece the Marvel Superhero Edition came with). But it is only compatible with the Disney Infinity 3.0 software.

Will this allow Hulkbuster to play with my Mavel 2.0 set?

No. This is a "play-set" for use with the Infinity 3.0 software which needs to be acquired separately. Both this "play-set" and the Hulkbuster are for use with 3.0 and not 2.0

can any 3.0 sets play with a wii system; not a wii u?

No, the only Disney infinity characters that will work with the wii are the 1.0 characters. To use the 2.0 or 3.0 Disney characters you will need to use the wii u and its platform/software or one of the other game systems that are supported.