The original working holiday visa is an “open work permit” meaning that it enables you to travel and more or less work freely throughout Canada, for a range of different employers.
The International Co-Op (Internship) and the Young Professional categories are “closed work permits” or “employer specific work permits”, which each come with a very specific set of requirements to be eligible.
Working holiday applicants do not need to secure work prior to their application, but young professional and international co-op applicants do.
International Co-op work permits are available only to individuals currently enrolled in post secondary studies, who are required to complete an internship as part of their course curriculum back home. Your work must be clearly related to your field of study, and you may only work for your previously arranged employer.
Young Professional permits are aimed to professionals. In this case, you will be required to prove that your job offer meets the TEER category 0, 1, 2 or 3 of the National Occupational Classification (NOC) and that it compliments your qualifications, creating valuable experience that will aid your career development.