Hi Jonsey,
I came across your ancestor John Cross in the Don Jail in Toronto fom August 6 138 to Sept 13, 1838. It stated he was jailed for Desertion under the authority of Co. Mausell (not sure how to read could be Maxwell or Maitland. On the September he was sent to Quebec City for transportation. With him were also Timothy Henlry and John Baker. On the next page, were another bunch of soldiers from the 34th Regiment of Foot. But it looks like Col. Maunsel was with the 85th Regiment of Foot.
By the way, if you suspect or know that your ancestor was court martialled in Fort Malden, Amherstburg in Ontario, you should contact them. I am told they have an archivist there who does research on soldiers who came to Fort Malden during war of 1812 and Rebellion of 1837. There is a good chance this person could help you locate records of John Cross. The Archives in Fort Malden would probably have records of the court martialled. I am told they are very good and friendly.
http://www.pc.gc.ca/lhn-nhs/on/malden/index.aspxYou can send an email or phone.
http://www.pc.gc.ca/lhn-nhs/on/malden/contact.aspxhere is some information about the 85th from rootsweb
The third 85th (Bucks Volunteers) was formed in 1793 and was posted to Jamaica from 1803-08. It was dispatched to America from the South of France in 1813. It was present at the battle of Bladensburg and capture of Washington, and in the attempt on New Orleans, where it suffered heavily. It returned from America in 1814. The regiment served in Canada from 1835 to 1842, during which time it was one of the regiments dispatched on horse-sleighs from New Brunswick to Quebec during the Canadian Rebellion of 1838-9; and afterwards served in the West Indies from 1842 to 1845. June 1838, three companies of 85th Regiment arrived in Upper Canada, remaining companies arrive in December.
Good luck