Why might an auditor choose to test a sample rather than the entire population of an account balance when performing audit testing?

Which Canadian auditing standards justify the lower level of assurance obtained when using sampling rather than testing the entire population? Cite the relevant section of the standard$($s$).$

Does the auditor$$s report provide any indication that the assurance obtained is based on a sample of less than $100\%$ of the population? Cite the relevant section of the standard$($s$).$