According to the Steam page, the game will be released on the 23rd of April. The game is also going to be coming out for XBLA on Xbox 360 and PSN on PlayStation 3, but no release dates for those platforms have yet been announced.
Poker Night 2 Date Set, Available for Pre-Order 09 Apr, 2013 / 0 comments
Steam now has Telltale's Poker Night 2 up for pre-order for Mac and PC for $4.99 USD (and with a free copy of the original Poker Night, giftable to a friend if you already own it).