Now this is kind of funny. I bought my Minolta CLE 40 f2.0 because, at the time, the Canon 35 f1.8 was out of my price range.
A few years ago (like 4 or 5), your lens was the more expensive and desirable of the two, running anywhere from $100~$200 more than a Minolta/Summicron 40. I think that if you search through the RFF threads on non-Leica 35mm lenses, you'll come to the conclusion that the one you already have is the one to get.
The multi-coated CLE Minolta 40 f2.0 is amazingly flare-proof. That point, for sure, is better than either the Summicron 40 or your Canon. If flare is a big issue with you, then get the Minolta (not the Summicron-C). However, be warned, the M2's 35mm framelines are just slightly too tight for a 40mm lens, you'll have to think "inside the box" on every shot. I know 'cause I have an M2. I also have an M6, the 40 is fine with that.
If I was looking for some real Leica glass to go on my M2 -and I already had a superb 35mm lens - then I'd be looking for a nice dual-range Summicron - with or without the "glasses".