Hey jktokyo,
the receipt number doesn't usually work until you get approved as a sponsor. So for now, if you have sent it with registered post, it's probably the only way to know if it has arrived or not. If you sent it from outside of Canada, you probably have a tracking number - you can follow on the national website first, and once the package has left your own country, with the same tracking number you should be able to track it on Canada Post website.
Other than that - you might get lucky and get an AOR ( Acknowledgement of Receipt) from Mississauga when they open the package, but most applicants don't, and the first time you hear from them is when you get the sponsorship approval.
Good luck with your application,
Sweden