The easiest way is just to call their customer line: 1-800-MY-APPLE. If the item hasn't yet been shipped, you should be able to cancel with no complications. If it's shipped, check their policy page for details on how to return the item:
Again, best to call them. The iTrip might be a special case due to your country's broadcast laws: I know it's illegal in the UK, for example. If so, they're not gonna ship it to you.
Duff-Man says....many 3rd party products sold at the USA Apple store are not on the Canadian store. The iTrip is made by Griffin is it not? Try their website and see who their Canadian dealers are....or try at MacWarehouse.ca - they carry it for about $50cdn Ithink.....oh yeah!
and as buying from the Griffen site...they want to charge me 22 bucks to STANDARD ship my item...and what makes it more outrageous, thats 22 dollars US! LOL
I got one from eCost.com..its only 30 bucks US! plus 7.50 shipping! what a deal! AND they are shipping on October 15th..even faster than what the Griffen site says! YAY
plus, they promise that there will be no duties cause of this program they have..its actually very Canadian-Friendly LOL