I traveled (travelled?) around the Big Island of Hawaii the last two weeks and found that--even at Volcanoes National Park--I could not escape thinking about writing. This text grabbed my attention on the Sulphur Banks trail:
It appeared on this large, instructive sign:
Why deal with spelling in a national park? Because on the Sulphur Banks trail, the park needed to explain the nature of sulfur.
When you think about whether to use U.S., British, or Canadian spellings, think about your audience. When I offer classes in nearby Vancouver, British Columbia, I always update spellings, and I consider using the word brackets for what I normally call parentheses.
This Oxford dictionaries page can help you with the basics, and this list covers most spelling differences--although not sulphur and sulfur. For Canada, a gray area (or grey?) when it comes to choosing between U.S. or British spelling, I consult The Canadian Press Caps and Spelling guide.
One word is always spelled the same way: the Hawaiian word and feeling of aloha.