Traditional proper Canadian spelling is a mixture of British and American spelling. For example, it includes forms like “colour”, “centre”, or “defence” (British) but also forms like “tire”, “curb”, and “aluminum” (American). However, there are many Canadians who use typical American spellings, such as “color”, or who mix up the forms. In the Toronto area, I have seen numerous signs which include the forms “color” and “center”. There is even a mall called “Centerpoint” (since 1990; originally called Towne and Countrye Square).
I don’t remember what I did in school, but at least since university, I have deliberately written “color” and “center”. I do this simply because it’s more phonetic (I.E., one less English spelling quirk), and therefore I see these as forms to be preferred.
I write “defense” (not “defence”). On the other hand, I don’t remember having ever spelled “practice” as “practise”.
I vacillated between “gray” and “grey”. I eventually settled on “gray”, which I recently learned is apparently the American form.
On the other hand, I deliberately double the “l” in past forms, e.g. I write the past form of the verb “level” as “levelled”, not “leveled”. The reason for this is that I respect a certain consistency in spelling. Doubling this consonant is in line with a common, but not universal, pattern in spelling: in many words, if you have a consonant sandwiched between two vowels, the first vowel is pronounced like its name, not like its sound. So compare “pop” and “Pope”. That’s why the past of “pop” is “popped”. The doubled “p” cancels out the vowel-consonant-vowel effect.
I write -ize, not -ise (e.g. “jeopardize”, “realize”). As I understand, that is in line with Canadian spelling and the “Oxford” standard of British spelling.
If my writing were subjected to further scrutiny, it’s a question whether more American forms would be found in it.
Other Canadians: how do you spell? Do you take care to write in a strictly “Canadian” way or are there American forms in your writing? Those that prefer forms like “colour” or “centre”, do you consider those to be proper out of patriotism? Or simply out of consistency?
A final interesting note: “harbour” is the British and standard Canadian form. However, the Toronto Harbour Commission Building, built in 1917, has “TORONTO HARBOR COMMISSION” engraved on it. Moreover, I have seen “harbor” written in a 19th-century issue of the Canada Gazette (I think in an Act of Parliament).