It looks like the North American version of the Sony Ericsson Xperia arc is soon set to go on sale. The LT15a version (as opposed to the LT15i European/Asian version) has been spotted for sale on ebay, two weeks before Rogers Canada is expected to stock the handset.
The packaging is exactly the same as the European version, but as you can see from the sticker below this is definitely the LT15a version, which means it will work on AT&T’s 3G bands. There is no official carrier for the Xperia arc in the United States right now but hopefully that will change shortly.

Thanks @SifosiD!