Romney has said he would work to pass immigration reform in his first year, but his definition of reform differs significantly from Obama's. He does not favor a pathway to legal status for most of the 12 million undocumented immigrants. Instead he said in January that he would back a "self-deportation" strategy that would implement enforcement laws designed to make life tougher for undocumented immigrants in the U.S., and thus cause them to leave on their own.
He's also said he would veto the current version of the DREAM Act, which failed to pass over Republican opposition in 2010, but would back some sort of "permanent solution" for young undocumented immigrants that would include a pathway to legal status for those who serve in the military.
Whether Obama is able to accomplish comprehensive immigration reform in his second term truly depends on a few things: his willingness to spend political capital on the issue and the makeup of the next Congress. But it's clear that Obama is staking much of his reelection on the issue of immigration and whether he delivers will be a significant part of his legacy.