Don't buy from Canada, even if he is a reputate seller. Theres too many fake ones in Canada. The authentic version is already sold out long time ago, just move on and buy the new ones off Mr Porter, Luisaviaroma, Bergdorf Goodman, Barneys, Far Fetch. Ebay is too risky, and who know someone might have bought a fake version and thought it was real?
No seller will simply risk listing Givenchy T-Shirts for 99 canadian dollars onwards. Who would do that? A seller will know that Givenchy T-Shirts are valuable and high in demand, each T-shirt sells for $400-800, they wouldnt simply put low prices. I generally avoid Canadian sellers, too many fakes that list as real.
There are two european sellers that are selling Givenchy, one in Cannes, and Netherlands.. they have stores in europe. Look up at their feedback as a seller, you get to save some money than buying in the states. But then again, think about what if the t-shirt you receive is defective and you have to pay for expensive returns, it could take 30-45 days to get your money back. Not worth it.
Best is still Mr Porter. I bought my Birds of Paradise T-Shirt from there for only £358 with free dhl express to Australia.