go with Panasonic, they are made in Mexico so there will be no duty, just 12% for GST + PST. personally i think that LCDs suck balls and plasma TVs are the only way to go, way better colours and blacks... unless you have a room where direct sunlight will hit the screen and cause glare. also dont buy into that 120hz or 240hz crap... we have been watching film based video forever and motion blur is natural to the human eye, all these technologies try to counter motion blur.
keep in mind that you have to pay exchange, about 18-19% when using a credit card these days. check out Costco.COM, they have way better deals and selection than Costco Canada and you can go to the ones in Washington to pickup your product and save on shipping fees. also tax in Washington state is 8-9%. if you do plan to have your TV shipped then check out these guys, they are great!!!!
http://www.pacificmailandparcel.com/
warranties are another issue, Costco might be a great choice because of this but i am not sure so make sure you call first and ask. as for straight manufacturer warranties those will vary, do your research first!
also one more way to save money is to forget about 1080p, just get a 720p plasma and call it a day. if you buy a 50" or smaller TV the difference is pretty much impossible to tell when sitting at the PROPER DISTANCE FROM THE TV. at this distance the human eye can not tell the difference, if you sit closer than you should, closer than what the manufacturers recommend, then YES you will see a difference. in the stores you will because you are always standing very close, at home with a proper setup you wont. if you are buying a TV that is larger than 50" then 1080p is a must, at that size range you WILL see a clear difference.
also think that one more expensive TV may look better in a side by side comparison but when you buy just one TV and take it home it will look awesome, even more so because you are not comparing it side by side to another model that is $1000 more!