2 external monitors with Macbook Pro
According to MacBook Pro (15-inch, Mid 2012) - Technical Specifications, this is what's supported under Graphics and Video Support and Thunderbolt digital video output:


  Graphics and Video Support
  
  
  Intel HD Graphics 4000
  NVIDIA GeForce GT 650M with 512MB of GDDR5 memory (15-inch 2.3GHz configuration) or NVIDIA GeForce GT 650M with 1GB of GDDR5 memory
  (15-inch 2.6GHz configuration) and automatic graphics switching
  Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to   2560 by 1600
  pixels on an external display, both at millions of colors
  
  
  Thunderbolt digital video output
  
  
  Native Mini DisplayPort output
  DVI output using Mini DisplayPort to DVI Adapter (sold separately)
  VGA output using Mini DisplayPort to VGA Adapter (sold separately)
  Dual-link DVI output using Mini DisplayPort to Dual-Link DVI Adapter (sold separately)
  HDMI audio and video output using third-party Mini DisplayPort to HDMI Adapter (sold separately)