It only takes a single stamp. But it does have to be the correct denomination. Currently the rate for one ounce from the US is to Canada is 75 cents.
One 54c stamp
It takes 42 postage stamps
2
The number of stamps must equal the amount of postage. The postage depends on the weight and and form of transport.
One if it is enough postage.
One.
The stamps have to add up to 45 cents.
one
20 stamps
You can buy postage online from the USPS government web site. You can purchase stamps for international postage at any post office. And many stores sell postage stamps at their customer service desks. Any US stamp can be used to mail a letter to Canada, as long as the total value equals the 75 cent cost for the first ounce of a normal envelope.
Just one.
umm 1000