Its not difficult to get into Australian uni's, over here you don't need a personal statement, interview etc. you just need to get the required grades. I think universities in USA and possibly canada are more difficult to get into. If I were you, I'd want to go to the USA, they seem to have some really good universities. Hope that helped somewhat
Canada is not that hard. But I know the US is quite hard. It depends what course you are studying. For example, the admissions for Canada, you need A-level English for arts, humanities, and those kinds of courses. Science, technology, and those kind of hard stuff you need A-level Math, Physics, Chemistry, or Biology, and English. They will look at your GCSE grades though. But they will concentrate more on the A-levels.
It costs a bomb though, and unless you're a national or have citizenship over there you can't actually work.
As for entry quals, it's difficult to say. The US has (iirc) well over four thousand four-year colleges, with a subsequent wide range of requirements. Some, like the Ivy League along with MIT, Stanford, Caltech and a number of smaller liberal arts colleges are extremely difficult to get into. Others, such as some state schools, are less demanding.
Also, don't assume that American schools are impossibly expensive. Many have significant scholarships for overseas students.
For Yale you will need to take the SAT test, and for Harvard you will also require 3 additional SAT II tests, which will certainly be looked on favourably by Yale if scores are reported.
However, you need to consider what you hope to obtain from studying abroad:
1. Should you want to go into any form of professional employment the American route generally stretches it out.
2. Should you want to go for PhD/research career your studies will be significantly stretched out; most American students coming to Britain have to take a senior status BA because of the broad nature of the courses
3. Drinking age in America is 21. This gives rise to a completely different college experience, which many british students, after two or even three years drinking in pubs find unbelievably immature.
However there are some real plus points
1. The sheer wealth of the top colleges gives rise to superb facilities. What is interesting is how this is spent, compared to say at Oxbridge.
2. The chance to take a very broad range of courses to such a high level is academically fulfilling
3. The experience of studying in a whole other culture [without any langauge difficulties] is rewarding and broadens the mind
4. Extracurricular activies, especially sport and student journalism are given such high status that they are particularly rewarding.
Hope this helps...
by the way...
what subjects are you most interested in doing?
what kind of grades are you looking at getting?
Harvard and Yale both operate 'needs blind' admission policies where you are accepted BLIND of you ability to NEED financial aid.
It is Harvard and Yale that define what constitutes need, and they determine what they consider you are able to pay, based on your family income.
Also, 3 B's might work for some American universities, but most likely would leave you well short of Yale's or Harvard's requirements.
I certainly don't mean to put you off, just to make you aware of the difference.