The "he" that this question refers to is the cloud. A major component of this poem is that Shelley personifies the cloud and makes it equivalent to a person. As for who the cloud is speaking to, that is up to individual reader interpretation. The cloud does not make an announcement that formally states who he/it is talking to. I've been through this poem a number of times in my career, and I still think that the cloud is speaking to a general audience. I often picture the cloud speaking to a classroom full of students. Maybe those students are regular attenders to the cloud's class, or maybe the cloud is a career day guest speaker.

The second option makes a lot of sense to me because the cloud spends much of the poem explaining what he does over the course of a day, night, season, and so on. I've never gotten the feeling that the cloud is speaking to a superior and trying to justify its actions. Rather I feel that the cloud is speaking to a neutral audience that doesn't really know and understand who the cloud is and what he does.