Difficulty depends on what you are good at and your interest, motivation and goals. I did a major in management, sub majored in employment relations [HR].
Like LaraB said, if youre after HD's, you need to do alot of work, research and have the skills required to be critical, analytical and write in an eloquent and original way.
HR i felt was much easier for me than management, especially exam time as they usually tell us the topics in the exam, in management, they do so but they dont have very good lecture notes as the HR lecturers. But both require more skills in english rather than mathematics, so reading, snythesising, arguing, understanding differing perspctives etc. are requirements.
but if you want a job, management is not a great go, its interesting and helps you understand business in its way [just as other majors focus on different ways a busienss functions], you cant go into management without experience, so note that. otherwise, management is very theory based, lots of reading academic texts [like really academic stuff that makes you think wtf am i reading?]. I felt that HR, though limited in my expreince of the study, had more easeir texts t oread, and therefore added to my interest.
if you want to know the available sub majors, check the degree you want t osub major in, e.g. if oyu like accounting, check B. Bus Accg in the handbook, scroll down and they should lael it for non-accg students the units to do.