At the post office. Order them online.
No, US post offices do not sell Canadian stamps. Canadian stamps are issued by Canada Post and can typically be purchased at Canadian post offices or through their official website. If you need to send mail to Canada, you can use US postage or go to a local retailer that sells international stamps.
First Class postage to Canada would be $1.50 as long as the letter is not over 3.5 ounces ... for heavier letters or packages, see the Related Link below.
3 stamps!
4 stamps
yes
US postal stamps can only be used for letters that are mailed in the US. If you are mailing a letter in a European country, let us say France, they you need to use French postage to mail a letter to the US or any other destination.
There are 15 stamps. 8/15 came from the US. 4/15 came from Mexico. 3/15 came from Canada.
It takes three stamps to send a letter to Norway.
3 stamps.
Yes
It takes 98 cents to send a letter to Brazil from the US
Yes, that is how it would work. You use the stamps of the country in which the package or letter originates. The Universal Postal Union sets the standards and coordinates the transfer.