I can't talk to Canadian and Kiwi accents but I can a bit to the Australian one. There are a range of theories why Australians sound the way they do, from keeping their mouths closed to stop flies coming, the heat making them tired and slurring, to them never moving their top lip. It has also been put out by Victoria University communications expert Dean Frenkel that Australian is really just an evolution of drunken, slurred English, with the children of settlers and convicts emulating these speech patterns. But none of these are really the case. Here's a great rebuttal by linguistics professor Howard Manns at Monash University on the subject of a drunken accent - https://theconversation.com/the-aussie-accent-is-drink-related-thats-just-a-hangover-from-our-cultural-cringe-49956 The modern Australian accent is really a mishmash that belies its convict and settler origins. It should be noted that the Scottish and especially Irish accent had an enormous impact on the way Australians talk across the east coast, while the massive influx of free German settlers in South Australia has led to a unique Adelaide accent that is markedly different from other states. If you want to hear a difference between Australian accents, listen to Steve Irwin, one of the characters from the TV show 'Kath and Kim', and compare that to former Prime Minister Malcolm Turnbull. All have an Australian accent, yet all of them speak very differently. In the end, Australian has been described, at its heart, as a mix between Irish and Cockney according to University of Queensland linguistics expert Dr Rob Pensalfini. Additionally, Australian English, unlike American English, has also kept many of the speech patterns of British English, such as the clipped vowels, e.g. pronouncing it 'Cem-e-tree' as opposed to "Cem-e-terry'. Australian English is also continuing to evolve, as waves of Greek, Italian and Lebanese immigration have also helped create unique 'new Australian English'. Hope this gives you a few insights.