I use only Polar bottles and they work great. Metal canteens will make the fluid way hotter then plastic unless the metal is a vacuum insulated unit, then you have a heavy bottle. The only problem with Polar is that the largest is 24oz. But you already have two sets of mounts on your bike for that style of bottle and you can get a third bracket that will mount a third bottle to a handle from Minoura; see:
http://www.minourausa.com/english/accessory-e.html scroll down to bottle cage holder and you'll find different brackets for different applications. Most LBS sell Minoura or you can go on line.
You can also get a 70oz Camebak if you need more water. 70oz is light enough not to become a pain on the back but enough fluid to last a while; see:
http://www.camelbak.com/sports-recre...cks/rogue.aspx