As a Canadian, I can firmly tell you that we use a wide blend of British and American spelling/pronunciation. Basically, any word in English derived from French that ends in '-or' or '-er' usually keeps the British spelling (think colour, honour, and centre) but it isn't unusual to see the American spelling for these words. We do spell a lot of things the American way, liked using '-ed' endings instead of '-t' for conjugated verbs (like 'burnED cookies' versus 'burnT cookies'), but I've seen people write with both endings. Endings with '-ize' are a little more complicated, because we tend to use both interchangeably and it depends on the person writing and their preferences and tendencies.
Really, when it comes down to it, we Canadian's aren't too picky. In elementary and high school teachers tend to favour the British spelling of words, but otherwise, it doesn't particularly matter to us. Written English is written English; we understand it whether you use American or British spelling. Use whichever spelling you'd like - I know that I use a healthy mix of both.
(And yes, we have 10-story buildings and 10-storey buildings. It depends on who's writing the words, but I personally use 'storey'.)