1, you can find checklist online, it published by canada embassy on its website, include in the file of "General Instruction" or " Section 3", I can't remember exactly which one is. Be sure place all your documents in order according to the checklist!
2, if you can't find mailing label in your local post office, prepare some big envelopes with your mailling address written on it is also acceptable, or otherwise, the embassy will use their own envelope, it's not a very important issue.