The standard Canon DSLR sensor setback distance is 55mm. That is the distance from the base of the T-Adaptor flange on the camera to the sensor surface. Your scope must be able to come to focus at the camera sensor. I assume you are using a standard EOS T-Adaptor bayonet fitting and something like the Bintel T-Adaptor, like these:
http://www.bintel.com.au/Astrophotog...oductview.aspx
http://www.bintel.com.au/Astrophotog...oductview.aspx
If setup using these, simply put the 2" adaptor into your focuser, with the flange right against the focuser tube top flange.
Try this first without a Coma Corrector!
Now as to Coma Correctors, ones designed for visual use may not be suitable for camera use. They have specific setback requirements. I have found the best coma corrector for use with Canons standard 55mm setback is the Baader MPCC (Multipurpose Coma Corrector). As it comes out of the box it has the precise setback you need for a Canon. I personally could not be bothered fooling around with other coma correctors that require spacers to get it right.
So come back here after you have tried to attain focus without a coma corrector, that is step one. If you cannot attain focus with just the scope adaptor, and you think you need more in-focus range to do so, then the solution is usually to move the primary mirror up the tube slightly (often this can be done within the range of the adjustment screws supplied). You can get as much as 5mm this way, maybe more, but you don't want to adjust it out so much that a mirror ring screw comes loose, you still need to be able to lock it. You can get longer primary screws, stronger and longer springs, etc if you need more range.
If a scope is being sold as an imaging optimised scope, then the focal length should already be setup to be able to attain focus IMHO. However, don't muck around with moving the mirror until it is clear that is the last option.
Finally, I don't understand your comment about a 2" to 1" adaptor, because that should have no place on the imaging train setup for a DSLR. You want to be 2" all the way into the camera.