Pandemic HR: Canada Emergency Wage Subsidy Calculator for Employers
Here is a tool that Dee Enright of JEBBCA strategies + holdings shared for employers in determining the Canada Emergency Wage Subsidy for March 15, 2020, through November 21, 2020.
From Punchcard Systems and Video Tax News, here is a great tool for employers and payroll administrators: Canada Emergency Wage Subsidy 2.0 Estimator. 
How much can I get?
This tool estimates entitlement to the Canada Emergency Wage Subsidy (CEWS 2.0) for periods 1 through 9 (March 15, 2020 to November 21, 2020). In general, the subsidy is determined by multiplying the percentages calculated below by the eligible remuneration paid in respect of the applicable period (to certain limits).
The rules for calculating the subsidy changed after Period 4 from an “all or nothing” system dependent on a 30% decline in revenue “original system”, to a scaling system (comprised of a top-up subsidy and base subsidy) available from the first dollar of revenue decline “new system”. Periods 5 and 6 are transitional, providing the higher of the claims under the two systems.
Important: The rules for calculating specific subsidies and eligibility are very complex and dynamic. Professional assistance should be sought. See Disclaimer.