The following link gives a decent overview of the four potential candidates. Mahmoud Ahmadinejad and Mir Hossein Mousavi, a reformist, are the two leading candidates but neither are shown as a clear front-runner.
As for foreign policy, all three opposing candidates have expressed disagreements with Ahmadinejad's foreign policy so there should be change in regards to that no matter who wins. All four candidates are going to continue the nuclear program and neither of the four have openly declared the need for military action against Israel.
http://www.foreignpolicy.com/story/c...?story_id=4989
Two articles about the election process in Iran:
http://www.cfr.org/publication/19593...breadcrumb=%2F
http://www.cfr.org/publication/19494...breadcrumb=%2F
Article about Mousavi's influence of the Iranian youth population:
http://www.foreignpolicy.com/story/c...id=4988&page=0