[Bêthberry]

In part, the answer for Canada is also the various linguistic natures of the cultural groups--Scots, Irish, Ukrainian, German, Italian, Chinese, First Nations (with their own various languages), Dutch, Polish . Yorkshiremen came to Fort York (Toronto) but the Finns went north to Sudbury.

There is also the issue that even the English immigrants themselves did not come with one overwhelmingly similar accent. Given that accents can change, particularly in London, within mere streets of each other, that means there was no primary accent. Add to that there was no aristocracy which imposed its accent as the proper or authoritative one.

In contrast, Australia has developed its own distinctive accent, although I don't know how consistent it is over the entire continent. Perhaps Australia had less of a multi-cultural influx than Canada and the US? It seems to me to have maintained more distinctly English cultural expressions than Canada has. Australia was the destination for the major deportation of convicts from the UK in the eighteenth and nineteenth centuries, whereas that stopped for North America after the American Insurrection.

The issue is related to Tolkien's own interest in language change. Look at how he explained the changes in the elven languages, based primarily I think on his argument about the influence of geographical separation in what likely were pre-literate conditions. (Note I'm not saying the Elves weren't literate!) I should go check my copy of BoLT and other HoMes . . . . (And so much of what Tolkien wrote about language has not yet been published.)

As for movie accents in fantasy flicks, perhaps if there is a predominance of English accents that simply reflects the sense that fantasy belongs to early ages, the Medieval world, rather than the modern world. Blade Runner offered an interesting view of language change in an SF context.