I thought employers are allowed to hire whoever they want for the job. If this is the case, those Kosher restaraunts in LA and NY should be forced to hire non-Jewish cooks or something.
This isn't the case in Canada. It's illegal to discriminate on the basis of religion in employment... and this starts even before a person is hired. If you use a discriminatory process to decide which applicants to
interview, you can be in trouble.
What you're allowed to do is set requirements that could generally exclude people of one faith or another, but they have to be directly related to the job.
For instance, in the case of your Kosher restaurant, you could have as a requirement "must be knowledgeable in kashrut food handling practices and must be experienced in Yiddish cooking". Even though very few (if any) non-Jewish applicants would meet those qualifications, you can't make "must be Jewish" a job requirement.
As another example, even the Catholic schools here have requirements like "must have a good working knowledge of the Catechism of the Catholic Church", but they can't say that they won't hire non-Catholics.
AFAIK, the only job in Canada where you can make religion a requirement (legally, anyhow) is clergy.