I have a Canon 100mm EF 2.8 Macro lens (not an L series) for my 70D. I want a 2x extender, but am not sure what to get that will fit and work. I have not seen a 2x for a non L lens.
Canon's own teleconverters (which they for some perverse reason call "extenders") will only fit a limited number of long L lenses, as the teleconverter has a protrusion in front which has to fit into a similar recess at the rear end of the lens. This means that you can't use a Canon teleconverter on the Canon macro.
The good news is that there are third-party extenders that you can use. Not the Sigma ones as they have a protruding bit just like the Canon, but the Tamron/Kenko/Whatever (basically one and the same product, rebranded) are flat at both ends and will work.
(The usual caveats apply as to whether it is actually a good idea to hang a 2x converter on a given lens. But it will work. You will get 200mm f/5.6 lens-converter combination, probably best used at f/8-f/11 to regain some of the sharpness and contrast lost to the teleconverter.)