The Canadian system is federal meaning that although you would be qualified to teach in Ontario, you would probably not be entitled to teach in another province such as Quebec. I assume that Austrailia has a similar system but NZ might have a uniform standard because of the size of the country. The U.S. system varies from state to state. You can try to contact the individual educational authorities on the internet or write to the embassies in London for further information. The E.U. now recognises other E.U. qualifications but the hoops to jump through can be many and difficult.
Easier options are private schools and British overseas schools. There are also English only schools in Poland and eastern Europe. The PR China has a lot of English language teaching positions available. Remember to take local cultures and governments into account when applying. In the E.U. you have a wide variety of rights and privileges that you will not have in other countries. In some countries your employer may even keep your passport, and you may need an exit visa to leave.
Visas usually are dependent on receiving a job first, unless you apply for landed immigrant status. If you are young, speak English and have a degree, you will probably have no problems getting the points needed to get permanent residency in Canada, Austrailia or NZ. Discrimination based on medical issues and disabilites are allowed.
Finally, even if you want to live in say, Sydney, take a job anywhere (in the same province) so that you can establish a local work history which will enable you to move on.
good luck- this is my 3rd foreign country I have taught in!