The Family History Library has copies of many cemetery records from Ontario. See:
Cemetery Records of Ontario, Canada. 17 Volumes. [N.p.: n.p.], 1947-1967. (Family History Library book 971.3 V3ce; film 823644-48, 874379 item 7, film 1035565 item 10; fiche 6046793.) For an index, see:
Index to Cemetery Records of Ontario. Typescript, [1971?]. (Family History Library book 971.3 V3ce; film 824329 item 8.) This is an alphabetical list of names and locations of cemeteries in Volumes 1-14 above.
Known cemeteries in Ontario are listed in:
Ronnow, Verna, ed. Inventory of Cemeteries in Ontario. Toronto, Ontario: Ontario Genealogical Society, 1987. (Family History Library book 971.3 V34i; fiche 6111034 and 6111139.)
For tombstone inscriptions from more than half of the 4,000 cemeteries in Ontario, see booklets published by branches of the Ontario Genealogical Society and other organizations. See also the magazines in the "Periodicals" section of this outline.
The Ontario Cemetery Finding Aid website has a free, searchable database of over 2 million burials in Ontario. It can be searched by name, cemetery, county and town. Although it does not include any gravestone inscriptions, it can be used to locate graves in Ontario.
GraveMarkers site has photographs of some cemeteries. They are listed by County and Town.