They apply through normal job sites liked linkedin and indeed and are lucky enough to find an employer willing to go through the process of hiring them.
Alternatively they work for a company in their home country that has operations in Canada and their company agrees to transfer them to Canada on an ICT work permit.
Usually through ICT, and directly through employer. Some law firms or consultants may offer services and you pay $10s of thousands of dollars. Some of it is illegal when you read media articles.