Is it necessary to place Canadian stamps on the SASE, or are USA stamps allowed?

Danielle On 8/09/2016 I sent a letter, a picture, and a self addressed stamped envelope to: Danielle Panabaker "The Flash - Season 3" Central City Films 3500 Cornett Road Building C Vancouver, BC, V5M 2H5 Canada On 12/19/2016 I received my picture back signed!!! http://i1378.photobucket.c...