Important Dates

Sole Proprietorships and Partnerships
Monthly, by the 15th Remit the payroll deductions along with your portion of CPP and EI.
Last day of February File your T4 and T4A slips along with the related Summary form.
March 15 First installment payment of tax and CPP contributions for self-employed.
March 31 Partnerships must file a partnership information return.
April 30 File your T1 personal income tax and benefit return for the previous year. Pay any tax amounts owing (regardless if self-employed or not). Self-employed individuals and their spouses/common-law partner have until June 15th to file their returns.
June 15 Second installment payment of tax and CPP contributions for self-employed.

For self-employed, T1 personal income tax and benefit return is due.

September 15 Third installment payment of tax and CPP contributions for self-employed.
December 15 Fourth installment payment of tax and CPP contributions for self-employed.
Corporations
Last day of February File your T4 and T4A slips along with the related Summary form.
Monthly Remit the payroll deductions along with your portion of CPP and EI.
Monthly Pay installments of the current-year taxes, by the last day of each month.
2 months from your taxation year-end The balance of the corporation tax payable is due.
3 months from your taxation year-end For corporations claiming the small business deduction, the balance of the corporation tax payable is due.
6 months from your taxation year-end File T2 Corporation Income Tax return no later than 6 months after the corporation’s year-end.

(source: CRA. Important Dates)