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.
It actually costs $0.85 to send a letter to Canada, and the first class mail stamps are worth $0.45 each, so you are wasting a nickel extra using two Forever stamps than buying the right one. But if you have to go to the post office anyway, just ask them for an 85 cent stamp for mail to Canada.