Hey there,
Speaking as a fellow Canuck that has imported almost his entire home theater set up, I share your pain in getting any kind of electronics across the border. For some quick vendor suggestions, in the past I have dealt with Emotiva successfully (albeit not cheaply), the Audioholics web store, and B&H Photo and Video. I can't speak to any retailer on Ebay, but I would verify if the store is a certified reseller by checking the manufacturers website prior to purchasing anything.
My method of shipping has always been FedEx International Ground, and I have never had to pay additional duty fees beyond what FedEx charged me upfront. Admittedly, the rate they charge feels like extortion, but it has made the transaction smooth after that initial payment.
My understanding related to the tariffs is that some electronics aren't manufactured in the United States... well, more like almost all except a select few speaker/sub companies... and thus aren't included under NAFTA. If the item is substantially completed in the US (or however they word it) then it is exempt from everything except for GST/HST and the basic duty of 6.5%.
Another option is to check out used items from Audiogon or the like and see what kind of sense of humor the sellers have about shipping internationally.
Cheers,
Bill