In today’s advice, I am a total hypocrite:
Plenty of different styles, in terms of usage, are fine. You don’t have to write in Standard Midwestern US usage if it’s not your own dialect, or it doesn’t suit what you’re trying to do, or you just don’t want to. I would advise being careful about marking dialect in a distinctive way–it can be a valid artistic choice, but often is inaccurate distraction–but the most important thing is to be consistent.
That’s what I think with my editorial hat on, anyway. As a writer, well, I’m a US woman who grew up within sight of Canada, and along borders, conventions get … muddy. My “natural” usage is really a muddle and completely inconsistent even when it comes to the same words (-er looks better phonetically, but … eh). I mostly aim for standard US, but there are definitely ways that I can’t bring myself to break from Canadian.