In what sense are protist primitive & in what sense are they advanced? You can only upload files of type PNG, JPG or JPEG. 2  You can only upload files of type 3GP, 3GPP, MP4, MOV, AVI, MPG, MPEG or RM. 3  You can only upload photos smaller than 5 MB. 4  You can only upload videos smaller than 600 MB. 5  You can only upload a photo (png, jpg, jpeg) or video (3gp, 3gpp, mp4, mov, avi, mpg, mpeg, rm).
In answer to your question, you can use a Forever stamp, but it won't be enough on its own. The cost of a US Forever stamp is 49 cents, while the cost of a letter to Canada is $1.20. USPS also sells a Global Forever stamp, as others have noted. You can certainly slap one of those on a letter to Canada.
The annual federal duck stamp had a face value of $1 in 1934, jumped to $2 in 1949, and to $3 in 1959. In 1972 the price increased to $5, then up to $7.50 in 1979, $10 in 1987, $12.50 in 1989 and to $15 in 1991. In 2015 the price of federal duck stamp rose to $25. For every $15 stamp sold, the federal government retains $14.70 for wetlands acquisition and conservation, so very little gets lost in the system for overhead. Most state conservation stamps have a face value of $5.