So I put up the Prefixes in the 'Other Regions' section. You can see how they would work there for you, and see how they show up while browsing the forum as well.
I did not make this section mandatory, so you can still post without the prefix. I can make the BC/AB/Canadian Rockies mandatory, or leave it open as well.
Just would need the breakdown for each section. If going by wiki suggestion above, it could look like:
In British Columbia
C/C = Cariboo / Chilcotin
FV = Fraser Valley
H/FC = Hope / Fraser Canyon
MV = Metro Vancouver
Nor = Northern British Columbia
S2S = Sea to Sky
SC/GI = Sunshine Coast & Gulf Islands
TO = Thompson Okanagan
VI = Vancouver Island
In Canadian Rockies
BC = Kootenays & BC Rockies
AB Cen = Alberta Rockies Central (Banff & David Thompson)
AB Nor = Alberta Rockies North (Jasper & Willmore)
AB Sou = Alberta Rockies South (Waterton & Crow's Nest)
CP/E = Central Prairies & Edmonton
KC = Kananaskis Country
Nor = Northern Alberta
SP/C = Southern Prairies & Calgary
And I probably put some region in the wrong section, so I apologize in advance
Each section can have a Sticky for the breakdown so it's easy to find.