Every time I get my mind made up and set to buy the Ultras....I start looking at these Cantons...lol
For me, this is a no-brainer. The Canton Chrono SL or Vento is the better speaker, it has more detail and a better tweeter...However Accessories4Less does not have the great no-risk returns of the SVS Ultras!
What you could do is buy a pair of any of the speakers in the link below for surrounds! Assuming you are going with a gloss finish (white or black) for the Ultras, these will match well enough and they are more compact which I consider a plus for surrounds. That way you can dip your toe in the Canton water without committing your front 3. If you like a very laid-back speaker, these are probably not for you, but I have a hard time imagining you could ever regret them for surround duty!
www.accessories4less.com
Note: I "finessed" the link by filtering for Brand=Canton and specifying the price range to isolate the speakers which I recommend. Over time, as prices change, this link will no longer Isolate those specific models!