The Upper Canada Sundries, aka Civil Secretary's Correspondence are found at LAC (Library and Archives Canada) and at the Ontario Archives. They consist of 32 volumes on 14 reels of microfilm and are an assorted collection of, as the name implies, correspondence.
The main responsibility of the Civil or private Secretary to the Lieutenant Governor was management of correspondence. The Secretary ensured that it was acknowledged, referred onward or filed. Closely related were the duties of receiving and acknowledging Addresses, petitions, memorials and applications for office; transmitting Messages and public documents to the Legislature; and referring petitions to the appropriate public offices for opinion or advice prior to submission to the Executive Council.
Although the province of Upper Canada did not come into existence until 1791, supporting documents of earlier date have been incorporated into some series of its records.
The Sundries are filed chronologically. There is no name index but the wealth of genealogical information makes them worthwhile to browse through. They contain an assortment of such genealogical items as undated petitions, marriage certificates, land records, letters, petitions for land, testimonies during wartime, military records, petitions for mercy for those charged with treason, etc.
Following is one example which I found during a lengthy search of the Upper Canada Sundries. It concerns the daughter of my Loyalist Ancestor Isaac Van Valkenburg aka Vollick. It reads as follows with my notes inside square brackets [ ]:
Dated Newark, 14 May 1796.
Source: FHL 1683290 p. 137 of Civil Secreatry's Correspondence, upper Canada, Upper Canada Sundries 1791-1800 RG5 A1 Vol. 1A pp41-556.
It has some pretty amazing genealogy information! I have more proof that my Loyalist ancestor Isaac was in Butler's Rangers, that he had a daugher Catherine who married Albert Hainer before May 1796 and that Albert and Catherine had 5 children by that date. This document also tells me that Albert was also a soldier in Butler's Rangers and that Catherine's father has been approved as a Loyalist (as per her being allowed the title of U.E. after her name)
This leads me to more research - I would now hunt for petitions for both Isaac Vollick, his daughter Catherine and her husband Albert Hainer. They should all have applied for land as Loyalists and their petitions should be found in the Upper Canada Land Petitions.
And thus a new avenue of research opens for me. (As an aside, I have already done this research and have found many petitions for all members of the large family Isaac Vollick brought with him from New York.)