In the interview and at the offer stage, the employer's promises and representations, despite being merely oral, form part of the contract. The difficulty is to objectively prove that the employer unmistakably promised "a 15% increase in salary after the first year" or "one paid sick day per month." As with proving all oral promises, if the issue goes to court one can only tell the judge what oral promises were made and relied upon. These are called express terms because they were actually expressed.
Terms are implied by necessity to give business efficacy to the parties' intentions. Every conceivable item of agreement cannot be expressed orally or in writing. The courts will say what the parties must have agreed to, even if the parties themselves did not address the issue. Rarely, when discussing salary, for example, will the parties actually stipulate that the salary for local employment will be paid in Canadian dollars. Absent evidence to the contrary, a court will consider the context and respond "Oh, of course, they would have meant local currency." It would imply the term that salary for work in Canada is to be paid in Canadian dollars.
Some of the statutory protections, such as those in minimum employment standards legislation, are implied by law and form part of every individual employment contract. The intentions of the parties are irrelevant. Even if one wanted to, one cannot negotiate or sign away those rights. Most statutes prohibit waiver of them, with language like: "An agreement that this Act or a provision of it does not apply, or that the remedies provided by it are not to be available for an employee is against public policy and void." These statutory terms are justified by a widely-held perception that workers occupy a generally - and often significantly - weaker position when negotiating with employers. Employment standards, human rights, privacy, and occupational health and safety protection legislation all provide a floor or minimum basket of rights for all workers to enjoy on the job.