Corse Matin has an excellent guide book (in French) available at airports and newsstands. You get plenty of information online from the official Visit Corsica website - just click here #GT20. Alternatively a guide (also in French) can be be bought from online retailers such as Petit Fute.
The are twelve stages commencing in Bastia and concluding in Bonifacio in the extreme-sud. Typically anywhere between 5-12 days riding depending on how much time and energy you have. I'd recommend not rushing.
The route is well signposted and the guides have accommodation suggestions but be wary as out of the holiday season it will be more difficult to organise.