I had an MA SSHRC two years ago and the envelope was letter-sized, skinny with a single sheet of paper inside (folded in thirds). Also, I got my letter before my department let me know, but it's possible the grad studies department knew beforehand and it took a few days for the information to trickle out.
If I get a doctoral SSHRC I don't think I'll be celebrating exactly. If I get it, I'll have to decide whether or not to accept, decline, or defer because I have a complicated family situation -- but then again, who doesn't?