You could try S&R knives in Toronto (a few clicks from the Airport). Sean and Rodney will usually make deals so don't pay the first price you see.
www.srknives.com call the store or stop in if you are in Ontario. If the knife you are buying is legal in Canada then the store will likely have it. If a store has it there is no reason that customs will seize it. About the only knives Canada Customs will seize are switchblades (yes a spring and a button) balisongs (butterfly), push daggers, concealed belt buckle and knives under 30cm long that are disguised as another object like a pen or lipstick (sword canes over 30cm are OK)
Buying fixed blades and Spyderco/Benchmade type folders that do not fall under the above will not be seized since they are legal. You may get nabbed for duty tax though and it could cost 10-30 bucks depending on how much the knife costs. This will depend on:
A does the customs officer look at that peticular package at all
B does the description on the package make it a taxable item (tool,knife,gift)
C how much is the value
D does the officer even care that day
I have only ever paid duty on one knife coming from the USA, it was a KaBar 1226. The duty made the knife about the same price as buying one up here would be. Usually I save $$$ on most knives bought from the States, instead of going to a CDN store. If you buy multiple knives from a shop like S&R the deals get alot better. Last year I was quoted $250CDN for a Next gen KaBar kydex partially serrated, and $300 for a SOG Seal 2000. I got the KaBar for $69US from Brigade Quartermasters in GA and the Seal for $110?US at AG Russell. The KaBar was in a larger surplus order so I saved on shipping and the Seal was $230CDN to my door with 2 day FedEx. The Seal would have been $300CDN plus %15 tax plus$15-20 shipping from Toronto. So around $365 CDN VS $230 CDN from the US seller.
BTW the cheapest Spydies I have seen in ON are at Tetragon in Toronto
http://www.tetragon.ca/search.cgi?uid=1089810278&category=Knives & Tools¤cy=CDN
they have Benchmade too. I think they want a little too much for the Leathermans though (Waves are usually 65US 100CDN)