The agreement is meant to simplify trade and investment regulations. Here is the U.S. Government statement (click on statements by Obama, etc.).
http://www.ustr.gov/tpp

In November, Canada signified its willingness to join the Partnership negociations. It is hoped that Japan will enter the negociations.

The object is to eliminate unnecessary tariffs, standardize rules on origin, remedies, and sanitary standards, intellectual properties, government procurement, etc.