The cost of mailing a first-class letter within Canada went up to 85 cents today — a 35 per cent jump from the 63 cents it cost yesterday.But the 85-cent rate is only available if stamps are purchased in a pack. If you want to buy just one stamp, it will cost $1.ow 85 cents to post a 1st-class letter within Canada, up from 63 cents. CBC News Posted: Mar 31, 2014 10:34 AM ET Last Updated: Mar 31, 2014 8:26 PM ET. A Canada Post employee delivers mail in Ottawa. Canada Post is hiking the cost of postage stamps to try to stem soaring losses. (Chris Wattie/Reuters).