I am a sophmore in college i dont have the best grades. I was wondering what the chances are that i would fly a harrier for the USMC?
If you don't have at least a 3.99 then you should quit now.

jk, in all seriousness as long as you have the grades to get into the program then there is very little impact on your airframe selection. Obviously if you do not have the grades to get into the Marine Corps then your chances of flying harriers is pretty low. Take one step at a time and do your best, you may decide you don't want harriers once you get in or you may just not be cut out for it.
I will either be going to PLC or OSC i havent quite decided that yet. After i go through that and then basic training from my understanding you pick your MOS.
By OSC I am assuming you mean OCS, in which going to PLC will still be OCS so I think you mean PLC vs. OCC. If that is the case then you really have no choice in the matter. If you enter the program prior to graduating college then you will be PLC, otherwise you will be OCC.
As for "pick(ing) your MOS"...well I will just say that it is nowhere near that simple. Do a search on here for the following topics: flight school, primary, advanced (jets), API, TBS, MOS...well and just about anything else. Spend some time reading the posts and figure out what information you need yet.
What are the requirements to be a harrier pilot. Any comments will be appreciated
They are far more numerous then I care to write about right now...but here is the simplified timeline.
OCS -> TBS -> API -> Primary -> Select Jets/Rotary/Prop -> Advanced -> Select specific aircraft -> FRS -> Fleet...