Sorry homesoon, but I believe you're actually half-correct. It's somewhat of a pedantic point, since a PR will want to apply for a SIN as soon as possible, but you do not require one to start work. The employer is supposed to check if you have one, but it's not a legal requirement for you to have one before you can be employed legally.
As a PR you have the right to work in Canada, and you are completely entitled to start work before applying for a SIN. There is no requirement to delay hiring someone until after they have applied for their SIN, as long as the employer is satisfied they are legally allowed to work (Citizen, PR or valid work permit).
Many employers play it safe, and won't hire you until you show the SIN card, but that's not strictly required from what I understand. If a PR lands, and has an employer lined up already, there is no reason legally why they cannot start work the same day.