When you filed the income at line 104 as "other employment income" this was incorrect, as you were not employed...but rather self employed. You needed to report the income as such...and yes, self employed income is subject to CPP deductions. It is calculated on the Canadian tax return. You are also responsible for both the employee and employer portion of CPP. This means you are subject to 9.9% of the net income of your self employment earning less $3500 (the basic exemption).
