To mail a first class international postcard to Canada, you will need to attach $1.10 in postage. The maximum size for a postcard is 6" in length x 4.25" in height.
Mail and stampage is based upon the weight of the mail. As long as the letter is still light, you shouldn't need more postage.
No, a forever stamp cannot be used for mailing letters to Canada. Forever stamps are valid for domestic first-class mail within the United States only. To send a letter to Canada, you need to use the appropriate international postage, which typically requires additional postage. Check the USPS website for current rates for international mail to Canada.
I don't seem to have enough change for postage.
Yes it is. Check out Canada Post's Website http://www.canadapost.ca/Personal/ProductsServices/AtoZ/LetterServices.aspx#requirements and look under 'Sending Mail to Government Free of Charge' for a complete list of who you do not need to pay postage to write.
$0.50
One if it is enough postage.
98¢
7.2
As of 2013, it costs $1.10 to mail a letter (up to 1 ounce, or about 28 g) to Canada from the US. Rates differ depending on the size of mail and other mailing options. See the United States Postal Service website for more details.
It will tax approximately two days for mail to get from Salt Lake City, Utah to Detroit, Michigan. You do not need extra postage just because mail is traveling further in the U.S.
For most destinations outside the U.S., Canada, and Mexico, a letter weighing 4.3 ounces will need $5.45 in US postage for a "First-Class Mail International Large Envelope" rate. Priority Mail International, GXG, or Priority Mail Express International carry higher rates.