Yes - you need to notify your insurance carrier if you have an employee on site for sure - it could affect your premiums and there are different standards of coverage for customer liability verses employee liability in the workplace.

As Momof4 mentioned ... being the employer you would be responsible for the CPP, EI, Vacation pay and other contributions during that time frame - although since this is a 'short term' thing verses a permanent employer thing CRA might be able to point you in the direction of an employment contract wording where you as the employer agree to pay the employee MORE in wages to cover the CPP, EI and other employer contributions and they remit it themselves at tax time...I know a few people who've done it that way.