I think the above MCCG902 canister is lightweight, if you want a lighter canister then one of the 2 entry level Kenmores are very light. Entry level for Kenmores means it doesn't have tons of extra features. All of the Kenmores have the same power nozzle and suction power though. This Orange Kenmore canister is actually currently onsale for $115. An excellent cleaning, quiet power nozzle with rubberized wheels on power head, quick release wands, push button cord rewind.
One thing about Kenmore, only the orange and green entry level units have a universal hose end to fit just about any vacuum cleaner attachment. Otherwise the White, Blueberry, and Red and Blue Intuition models have a Kenmore exclusive line and only fit the tools that come with the machine which aren't very good.
Other canisters to consider would be Oreck Quest Pro, and Royal Lexon SR20. The Royal is a very nice unit and I've seen it on eBay at $299 BNIB. The Hoover Windtunnel Anniversary is ok. It cleans great, I think its a little heavier than the Panasonic, on/off switch is a little hard to use and is on main suction unit only, in comparison to Orange Kenmore, Panasonic and Royal where the on/off switch is on hose handle. Hoover hose handle is also not as comfortable to use and hose isn't very flexible. The Kenmore and Panasonic have Cen-Tec power heads with chevron brush with serpentine belts. On the Cen-Tecs the edge cleaning on the belt side of the power nozzle is awful and virtually inexistent. Hoover is chevron with stretch belt-- which actually on these units, they run fairly well for a while with out any noticeable loss in agitation. The Hoover has better edge cleaning than Cen-Tec power nozzles. I don't know the belts for the Royal or Oreck.
If you go to uprights I would recommend what IpreferKirby did as the Hoover Windtunnel Max bagged upright or a Panasonic upright.
Whatever you decide, I would skip bagless. Too much maintenance. You have to remove the dustbin and dump outside the house with every use, sometimes a few times in one day. Bagged units have power to compact dirt into extra large bags and you remove about every 3 weeks. Quick and pain less. Filters on bagged unit won't get near as dirty as quick as on bagless unit and machine in general will stay cleaner.
http://www.sears.com/kenmore-canister-vacuum-cleaner/p-02029319000P?prdNo=3&blockNo=3&blockType=G3