There is no “flat rate” calculation method for business, employment or rental related automobile expenses. To claim those expenses, you must have receipts with the actual costs, as well as a log book that records your business kilometers traveled. There is, however, a simplified way to do a logbook, but that only determines your business use of the vehicle.

T777 Statement of Employment Expenses (PDF)

https://www.canada.ca/content/dam/cra-arc/formspubs/pbg/t777/t777-15e.pdf

CRA page regarding Motor vehicle expenses (not including CCA): https://www.canada.ca/en/revenue-agency/services/tax/businesses/topics/sole-proprietorships-partners...