At least 6 weeks before travel
24 - 48 hours
72 hours before your flight departure
PCR covid-19 test is the most accurate and widely accepted test.
Countries are constantly changing their requirements so be sure to check with your airline which test is required. Currently the only country accepting the rapid antigen test is the USA
There are many countries in Africa and South America that require yellow fever vaccination for entry or are high risk of getting yellow fever. Check out this link as it is always getting updated https://www.canada.ca/en/public-health/services/diseases/yellow-fever.html