you will not get any advantage from Fedex, i had the same problem exactly with Fedex, in the same document exactly, police clearance certificate(looks like FEDEX has an allergy against police clearance certificates!), it was sent from my country to canada by Fedex and it has never been delivered to me, Fedex lost it and they are very good in escaping the results of their fault.
I had to use Fedex again to send my full application to Buffalo visa office from canada because there is no other choice. People say here that FEDEX is still the best courier company even if they lose shipments sometimes.
Actually all couriers are the same, they might lose shipments even canada post, i remember when i asked the guy in canada post about sending my application to Buffalo, he said that no one can guaranty that your shipment will be delivered 100% so i went with FEDEX again at least they are faster than canada post(with the same level of risk).
Have a look at this link (that was my problem with FEDEX):
http://www.canadavisa.com/canada-immigration-discussion-board/unfortunatly-bad-news-about-fedex-company-am-very-sad-t23429.0.html;msg125374#msg125374