Do you have his marriage registration information? If he married after joining the RCAF, there will be a service number. What year did he marry.
Also can you provide any details for all members of the family that you found on the 1916 census as I don't have access to it. The information would give province and town, occupations, ages, dates of birth and where born. (such as another country or province within Canada).
Do you think his brothers were older or younger than him?
What will be available will depend on the province that Donald was born in. There isn't a central registry in Canada, everything is by province.