According to the Dept of Canadian Heritage, post-nominals are used in certain situations to denote Crown honours, awards, medals and official appointments.
Post-nominals have a specific order or precedence, and it is also not always appropriate to use all of them, depending on your audience or situation.
For example, if you have a PhD and a Bachelor‘s degree, you normally just put "PhD" and not "PhD, BA" following your name.
Generally, the highest-ranking awards come first after the name, unless the courtesy title "Esq." is used. In that case, the post-nominals follow the courtesy title.
A British book, "Debrett‘s Correct Form", sets out the custom used in Britain and the Commonwealth for the use of post-nominal letters. It includes both civil and military use, and styles of address, etc., for people of different rank and precedence. The custom is similar in Canada, except that we have our own precedence because we have our own honours and awards, which do not include or recognize knighthoods.
The general ranking of letters after the name are as follows:
1. Orders and decorations conferred by the Crown.
2. Appointments to Crown offices, such as Privy Councellor (PC), and Aide de Camp (AdC).
3. Law appointments: Queen‘s Counsel (QC), Justice of the Peace (JP).
4. University degrees.
5. Religious orders, then medical qualifications.
6. Fellowships of learned societies, fellowships/memberships to professional institutions, and Writers to the Signet (WS).
7. Members of Parliament (MP) and Members of a Legislative Assembly (MLA) or Provincial Parliament (MPP).
8. Membership in one of the armed forces corps (RCAC, REME, etc).
All of these letters follow "Esq." if used. If the person is a Baronet, they follow "Bt." if used.
The precedence of the orders is set by CF regulation. The Canadian Forces Decoration (CD) is one of the last ones in the order of precedence. The Order of Canada had three ranks and it is the most senior Canadian order. Companion, the highest rank (CC), follows immediately after the VC and GC, unless the holder is a Companion of another more senior order (CH, CB, CSI, CMG), which isn‘t likely in Canada.
Check the DND website for the ranking of military honours.
Not all honours include post-nominals.
One thing I noticed is here in Canada, some people use "MID" as a post-nominal, to indicate a mention-in-despatches. This is actually incorrect. There is no post-nominal for this.