Will unitax auto zoom 85-210 fit a canon rebel

a 550D is a detachable lens camera and will not auto-zoom (it has a rubber ring that you turn to accomplish this with most lenses). are you sure you have an EOS 550D, or did you mean auto-focus?

Quantaray makes lenses with many different mounts. If the lens has a Canon EF mount then it will fit your camera. If it has another mount, Nikon for example, then it will not fit your camera.

Quantaray makes their lenses with a variety of mounts. A lens with a Minolta mount will not fit onto a Canon camera. A lens with a Canon mount will work just fine on a Canon camera.

Sigma makes their lenses with a variety of camera mounts. If you get the lens with a Canon mount then yes, it will fit any EOS Rebel camera body. A lens with a Pentax mount, for example, will not fit a Canon camera.

Just a thought - are your Image Stabilizer and Auto Focus switches On or Off?
Might be worth experimenting with them.
Otherwise, sorry, can't help.
May be necessary to contact your vendor.

focus ring on cannon ef70-300 zoom is stiff, jerky. how can i free it up.

change your manual settings

The 35mm Rebel Ti and the Rebel 300D use the same lens mounting protocol. All Canon cameras designated 'EOS' use the autofocus EF lenses. If your Quantaray lens worked on the Rebel Ti, it will fit and should work on the Rebel 300D.

You need to by one with a Canon EF fitting.

Quantaray is a private label lens made for Ritz Camera. They make this lens to fit several different camera brands including Nikon and Canon. The only ones that will fit a Canon camera body are the ones with the Canon EOS mount. If your Quantaray lens doesn't have an EOS mount, then it won't work on your Canon camera. You can take the lens to any Ritz Camera location and they can help determine which mount it has, and which cameras it will fit.