Nvidia uses sli. AMD uses crossfireX. Same idea but each company has their own method of combining two graphics cards to increase graphic performance. I think you are looking for an Nvidia sli ready card.
In your price range ( up to $170), I think you are looking at either a gtx 460 or Radeon HD 6850. The tom's review says you can get a gtx 560 or a 6870 for $170 but even the low end 6870's at newegg.ca are $180 and the price goes up from there. The 6850's and gtx 460's are rougly $150.
If you bothered to look you would have seen that the prices are the same on either site and depending on the day the value of one US dollar vs one Canadian dollar is the same and shifts from one side to the next by a penny or two depending on the current exchange rate. If I order from newegg.ca it still comes from a warehouse in New Jersey but having a Canadian website means that I will not be subject to import duties.
Yes, that was a fault on my part. I should have stated newegg.com and not newegg.ca. I guess not everyone is aware that the prices for technology and the value of a CDN dollar and a US dollar are essentially the same.
The only indication of the currency in question is that he linked .com and not .ca. He did not state 'US DOLLARS' as you mentioned.