The Historical Society of Pennsylvania provides electronic access to the 1763 journal of William Trent, a merchant and militia captain stationed at Fort Pitt during Pontiac's Rebellion.
The George Washington Papers held by the Library of Congress are available online. These include correspondence, journals, and military papers related to the French and Indian War.
A very useful collection of documents is available at ExplorePAhistory.com. These include George Washington's account of the death of General Braddock, and British General Jeffery Amherst's letter discussing the potential for using smallpox as a weapon against the Indians during Pontiac's Rebellion.