Hi all,
Is there any database that regroups phd projects outside the UK? Asutralia, Canada or US for example?

What do you mean by regroups???
Anyway try the PhD job adverts of Science
http://sciencecareers.sciencemag.org/feature/acad/acadsubj1.shl
and Nature http://naturejobs.nature.com/js.php

if you are in natural science.

You can have a look at New Scientist's web site http://www.newscientistjobs.com/splash.action and they have job vacancies and PhD research available there. Much like all PhDs though, you can always just write to a potential supervisor in an institution/area you're particularly interested in, but judging by the fact that you're looking for US/AUS/CAN proects you're not too bothered by the place you go.