It also helped that both of those colonies were much smaller, population-wise. The US population at the 1790 census (so, after a decade of population growth, but also after the emigration of the various loyalists) was just under 4 million. Canada wouldn't reach that population until the 1870s, and Australia not until the 20th century, by which time the British had far more profitable (and less white) colonies to try to mismanage, so granting them self-government was less of an issue (especially as the British had already reformed some of the worst abuses of their own government system to make it less unrepresentative).
Canada also had the advantage of a large, expansionist neighbor constantly threatening them (it's worth remembering that the 13 Colonies didn't start agitating against the crown until after the French and Indian War had eliminated the French as a threat).
But, as noted, the example of the American Revolution as "what not to do" in terms of managing a colony was very much in people's minds, both in the UK and in Canada/Australia. It's certainly worth comparing the reaction of the British government to e.g. the Canadian rebellions in 1837 to how they reacted to the much less significant Boston