As mentioned above, very limited income tax deductions are available for corporations with PSB income. The best way to get out of the trap of substantially higher corporate income tax rates is to pay the salary to the incorporated employee. If the corporation has nil or a lower net income as a result of this deduction, the corporate taxes will be zero or lower too.
Many incorporated employees end up paying 2X of CPP; one at the corporation level and another one at a personal level. So, an otherwise attractive contract might not be as attractive. One of the reasons many businesses require corporations to sign the contracts is to avoid remitting source deductions and other employment-related costs such as vacation pay.