Sandy asked "Looking for anyone related to Peter Wyckoff (1765-1797) who married Catherine Plato (1769-1856). Her second marriage was to John Clendenning (1760-). Want to prove Loyalist ties for these two. Their son Peter (1794-1881) married Abigail Gilbert (1790-1834) daughter of Isaac Gilbert UE (1742-1822)."
are 8 results for John Clendenning (and variant spellings) in the Upper
Canada Land Petitions online database.
To find out how to use the index
information to find and view the actual petition(s) online, see Searching Ontario Canada Land Records, eh?
You will also want to obtain the petition for Catherine Clendennan to see if it is Catherine Plato.
There are many Loyalist resources but you will want to start your search with these.