Canadian Tire's site is huge and they've got tons of items and categories available. They also got an "Online Only" section with items not found in stores.
Chapters.indigo.ca is the result of an Indigo takeover of Chapters in early 2001. Huge inventory. They're the big boy on the Canadian online block when it comes to books.
HBC (formerly Dealsoutlet.ca) is the online site for The Bay / Zellers / Home Outfitters / Designer Depot in Canada.
They don't carry everything the stores do, but they've got lots of deals going and lots of very "giftable" items -- plus some stuff that isn't even available in-store!
$5.49+*
Free shipping to the nearest The Bay, Zellers, or Home Outfitters
Sears.ca has some nibble-worthy deals on just about everything in their "Outlet". They use it to clear out old stock. They've also got "Today Only" deals and "Price Droppers" where the price goes down every week until they run out of stock.
The Sharper Image sells all those nifty gadgets you see on TV. Your orders will most likely be "dinged" with customs fees when it crosses the border, so factor in $5CDN+tax on top of the total.