The postage requirements are constantly changing, so it's best to double check the requirements if you're sizing is close to the minimum or maximum size.

For Canada: Canada Post website
For the USA: USPS website

Canada - postage requirements



cost of postage - within canada
standard lettermail (up to 30g) - $0.52
standard lettermail (30 - 50g) - $0.93
non-standard and oversize (up to 100g) - $1.10

cost of postage - to the USA
standard lettermail (up to 30g) - $0.93
standard lettermail (30 - 50g) - $1.05
non-standard and oversize (up to 100g) - $1.78

usa - postage requirements