In most apprenticeships you have to have a job before you become an apprentice or go to school.
I am fortunate in that I work in a family business, so my job is typically secure, or I can hope.
I know that if you're a union member, at least within my trade, your job is pretty well secure while you're in school. The Ministry of Training, Colleges and Universities mandates that the job is secure while you are in school, and you're not to lose that position.
It may be difficult to start out initially, but once you are an apprentice it shouldn't be that hard. You can jump from company to company.