The following Upper Canada Land Petitions are listed for Lancaster under the following spellings. They range from 1797 up to 1849. I would suspect the first two petitions, on the same microfilm C2193, would be the same person. I did not look up the 1826 nor the 1849 petitions. I have paraphrased what these say so you should check these yourself for accuracy. The 1819 petition concerns Con. 5 Lot 27, the one beside Con. 5 Lot 26 as is mentioned in your query.
Regarding the "taking of Quebec" & Fraser's regiment, during the Seven Year's War, mentioned in the 1797 petition, the Battle of the Plains of Abraham took place in 1759, so this fellow would not be your Donald born in 1765, more is here:
https://en.wikipedia.org/wiki/78th_Fraser_HighlandersMcDonald Donald Lancaster 1797 330 M 4 Petition 42 RG 1 L3 C-2193, pages 174 & 175- private soldier at the taking of Quebec in General Fraser's Regiment & afterwards in the 60th Regiment of Royal Americans, petitions for land Oct 10 1797, County of Glengarry; pg. 175 -he was asked for his discharge papers 28 Feb 1898
McDonell Donald Lancaster 1797 330 M 4 Petition 63 RG 1 L3 C-2193, page 246, 247: dated 10 Oct 1797, Glengarry County, so the same date as the above petition - served as a private Soldier in the Duke of Gordon's Regiment for three years and received his discharge. Has been in this Country for two years but has received no lands; June 14 1898- pg. 247 -petition for 300 acres as a Soldier
McDonell Donald Lancaster 1816 337A M 11 Petition 115 RG 1 L3 C-2199, pg. 324, 325, 326 - He is the son of Finnan McDonell of Lot 24 Con. 6 & has reached the age of 21 years & petitons for land in Oct. 1816. Received 8 Feb 1817 (my note: Finnan McDonnell was on the old UEL list as a Sgt. 84th Regiment)
McDonell Donald Lancaster 1819 341 M 12 194 RG 1 L3 C-2201, pg. 524, 525, 526, 527, 528, 529 - the petition of Donald M Donnell of Lot 27 in the 5th Concession of Lancaster, Yeoman. In the year 1791 he exchanged Lot 17 5th Con. Lancaster for Lot 27 with James Clark now of the Township of Charlottenburgh. The lot was received by James Clark from the late Lt. Col. John McDonell who claimed it as assigned to the late Lieut. James McDonnell. The petitioner immediately after the exchange with Clark took possession of Lot 27 and commenced his improvements & has been in possession of it ever since for 28 years. During the lifetime of the said Lieut. Col. McDonell the petitioner looked for a Title to this Property which was promised but without effect & that since his death the petitioner has heard this land had been marked as a Clergy Reserve. He is apprehensive that at the time he exchanged the siad lot No. 27 with Clark, he was under a mistake as to the number of the Concession , the same Lot in Sixth Concession & not in the Fifth being his property. Petitioner asks that Lot 27 marked as Clergy Reserve be given to him. James Clark stated Lt. Col McDonell claimed the said Lot 27 as assignee of his cousin the late Lieut. James McDonnell & exhanged this for Lot 17.
I did not look this one up:
McDonald Donald Lancaster 1826 349 M 14 543 RG 1 L3 C-2208
I did not look this one up:
McDonald Donald Lancaster 1849 318 Mc 5 62 RG 1 L3 C-2184
You can retrieve the microfilm online for the petitions here & read the originals by looking up the Petition number.
http://www.collectionscanada.gc.ca/microform-digitization/00...