Under the federal system, a brother can only sponsor a sister if she is under 18 and their parents are dead or in the case that the brother has no relatives in Canada and he has no other relatives alive that he could sponsor such as parents or children. Parents can sponsor children after 24 years of age if they are not married and are full time students since before the age of 22. See more info here: http://www.cic.gc.ca/english/immigrate/sponsor/relatives-apply-who.asp#who_can
Under provincial nominee programs, there are ways to sponsor adult children and siblings if both the sponsor and sponsored meet the requirements of the program such as having lived in that province for a certain amount of time, having a certain amount of money, meeting education/language requirements etc. The 3 provinces which have family stream components under their PNP's are Alberta, Manitoba and Saskatchewan and you can find out about their exact requirements at http://www.cic.gc.ca/english/immigrate/provincial/apply-who.asp
