Dancing in the Sky: The Royal Flying Corps in Canada’ by CW Hunt gives a useful outline.

See also: ‘Royal Flying Corps: Borden to Texas to Beamsville’ by William E Chajkowsky

Canadians (& Americans claiming to be Canadians) joined the RNAS in Canada in preference to the RFC as the RNAS shipped them to UK for training while the RFC expected them to get their tickets before enlistment. The problem with this is that there weren’t the schools in Canada to provide the training & paying their own paasge to Britain to train wasn’t a financial option for most. This is explained in ‘Canadian Airmen and the First World War: The Official History of the Royal Canadian Air Force’ by SF Wise.

Around the time you are interested in, a group of RNAS recruits were transferred to the RFC after arrival in the UK as the RNAS lacked the means to train them. So, he may have an RNVR service record.

If he enlisted before the formation of the RAF in April 1918 he would have a British Army and/or Canadian service record separate from his RAF record.

Naval officer records can be found on ‘Find My Past’ (accessible free in many libraries). Also check the London Gazette – https://www.thegazette.co.uk/awards-and-accreditation/resources?service=awards-and-accreditation&results-page=2 – for a possible army commission. You can check Army & Navy Lists (available in larger libraries & on National Libary of Scotland website – https://digital.nls.uk/british-military-lists/archive/). Canadian service records can be found at https://www.bac-lac.gc.ca/eng/Pages/home.aspx