FamilySearch adds Great Britain, War Office Registers, 1772-1935

This addition is from the (UK) National Archives in Kew, WO 25, which is a collection of documents of various kinds, including regimental descriptions, succession books, commissions, appointments, descriptions, returns of services, casualties, half pays, pensions, and gratuities.

Most are for the first half of the 19th century.

The indexed information is limited: typically name, event type, event place and sometimes age. More detailed information is in the image of the original record which is only available at FamilySearch authorized locations.

There's a long list of these WO 25 records here. Some are for the Royal Canadian Rifles from 1841 to 1870.

Also from WO 25, Ancestry has Canada, British Regimental Registers of Service, 1756-1900.