The sponsor does not need a job or an income to sponsor his or her spouse or common-law or conjugal partner. However, in this case, they should submit a plan with the application explaining how they will support themselves once the applicant becomes a PR.
It is very rare to be rejected because the visa officer does not believe the couple can support themselves without going on welfare, but it has happened. In one case I saw, the sponsor was a recent immigrant who had a job that paid less than minimum wage. His wife could not speak English or French, and was a teacher back in China. The visa officer did not believe that the husband could support both of them in Canada, and did not believe that the wife would be able to find a job, so the application was rejected for financial reasons.
Keep in mind that this is very rare. Usually a letter explaining how you will support yourselves, with proof, will be enough.