Things you need:
1.) Proof of status in Canada (Notice Of decision from IRB).
2.) Proof of ties to Canada such as assets, job, property lease, business ownership etc.
3.) 4-6 months pay stubs. Or 4-6 months bank statements if you’re self employed.
4.) Tax assessment for the year is very helpful as well.
5.) An invitation letter is an asset if u have family in the USA. Purely optional though.
These are the real documents that will most likely guarantee you success.
Good luck.