Saskatchewan here: http://www.saskimmigrationcanada.ca/family-members
Manitoba here: http://www2.immigratemanitoba.com/browse/howtoimmigrate/pnp/pnp-family_support.html
Your sister has to be PR or citizen and have lived in the province for at least one year before applying to sponsor you. She and you both have to meet other requirements of the program, for example with your education, work experience etc. SK is better because it only requires you to be 18. Manitoba has a minimum age of 21.