According to Variety, Marvel is looking for a lead in the upcoming Ant-Man film and their two front runners are Paul Rudd and Joseph Gordon Levitt. There is still a possibilty for more names to come later but those two are the only contenders for the main role at the moment. 

Edgar Wright has already been posting some photos of the production on his twitter, and even Marvel has moved up the date of the movie into the middle of the summer, not far off from the Avengers sequel. 

The sources at Variety mention that the two actors will be meeting with Marvel and Wright one more time before one of them is picked. I personally wouldn't mind seeing either one of them getting to play the role, but than again I don't know much of anything about the character of Ant-Man, so I'll be interested to seeing what they do with the movie, and the new approach they take on it. 

Source: Variety