The dual influence of British and American spelling on Canadian English can make life difficult for Canadian writers, and especially for Americans writing for Canadian readers.
Canadians use standard British spelling for certain words (axe, cheque), and use American spelling for others (connection, tire), and will use either version for other words (programme and program, labour and labor, neighbour and neighbor).
It's important to be consistent so you don't look silly and confuse your readers.
Set up your own style manual (just a list, really), and stick to it. Don't mix "neighbour" with "labor," for example. Choose one pattern or the other and don't vary.
A Canadian dictionary might help, too (is there such a thing?).
Word processor spell-checkers (chequers?) may not be much help. My MS Word rejects Brit spelling, and there doesn't seem to be a Canadian or British "language pack" available.
I could tell my PC to accept "programme" and "neighbour," but that would not make it reject "program" and "neighbor." To be safe, I'd probably have to search for all of the offending Americanisms and change them.
Or, I can just keep writing in American and not worry about countries with people who speak almost the same language.
I don't freak out when I encounter British spelling. "Programme" is not nearly as disconcerting as having to deal with quid, shillings, pennyweights, roods, Imperial gallons and barleycorn.
Biblical shekels and cubits are a pain, too.
(Thanks to Dorothy Turner for her work published by the University of Ottawa)