I used the Katadyn Befree system this week on Mt Whitney.  Great waterflow and great reviews.  It filters bacteria, protozoa and "crud" but not viruses. 

That said, if you're hiking the traditional routes at the Canyon (Bright Angel and/or South Kaibab and then going up North Kaibab, you won't need to filter water.  There's potable water at numerous places.  I do R-2-R frequently (live in Scottsdale) and will be there again in September for a R-2-R-2-R crossing.