Hello Aspirant

For admission to an Australian University, you need to have a bachelor's degree of 4 years, this is mandatory for foreign universities' admission into Master's courses. But many colleges also offer a bridge course for students who have done a bachelor's in a 3-year course plan.

The switching of streams will not be a problem, you can get admission to an MBA easily if you crack an aptitude exam (GMAT, GRE) and a language proficiency test (IELTS, TOEFL, etc.)

Hope this helps