Generally, people wait until they receive their permanent resident visa and are landed in Canada before starting their business.

You may be able come to Canada on a visitor visa while your permanent resident application is in process and research potential businesses and even buy a business in advance - but you may not work in the business without a valid work permit, so normally it would involve hiring a manager or other employee(s) to manage the business for you.

There is also some risk involved in setting up the business in advance, as you may not ultimately be approved for a permanent resident visa.