Pierre's right - you're going to have a heck of a time finding ANYONE willing to ship to Nigeria because of all the scamming there.
A suggestion (and it's not a very good one from your point of view) - contact the seller involved first and suggest that you are willing to pay by Canada Post Money order for the dress and shipping. That takes the possibility of scam out of the equation for the seller.
The downside is that you will have no buyer protection. If the seller messes up or the parcel goes missing, you'll have no way to get your money back.
Imagination will often carry us to worlds that never were. But without it we go nowhere. Carl Sagan