I don't have a Mac, and I don't have a 5D2, so I can't make informed comments about iPhoto or issues you may be having with the 5D2.
But I can make some general observations.
For instance, from what you describe, the fact that you get "better results" from tweaking your 5D2 files in iPhoto than you do in DPP, it actually sounds like your issue is with your processing software rather than with your camera.
For instance, when you talk about a "sharp image": there are two fundamental "meanings" that people use when they refer to "sharp". The first is "technical sharpness", meaning how the camera captures fine detail (using proper technique) and then how those details are "rendered", either in the camera when producing a jpeg or in your Raw processor. You view those details at 100% and can "tweak" your sharpening settings in your Raw processor to get good "capture"/"input" sharpening.
The other way people refer to sharpening is a "look", what people often refer to as "pop", of an image. This is actually more properly the result of Contrast and Saturation (along with Sharpening) that can be applied by your camera to produce a jpeg, or in your software, either to the jpeg or to the Raw file.
I suspect that it is that latest meaning of "Sharp" that you are referring to. In other words, it has less to do with your camera and rather has to do with your software and how you use it, which would explain why you see different results in iPhoto compared to DPP.
The thing is that you actually should be able to get significantly better results from DPP compared to the "generic" iPhoto. For one thing, the Canon software is "engineered" for the Canon Raw files/Raw data. For another thing, Canon has provided features and tools designed for their cameras.
But, it's up to you to learn to work with those tools!
For starters, I'd take time to play with your Picture Styles in your Raw tab. Different Picture Styles will have different default settings for your Contrast, Saturation and Sharpening as well. So, changing to different Pictures can make a significant different to the "look" of your images. Try it! For example, change to, say, the Neutral Picture Style, then to the Landscape Picture Style and check out the difference.
And then, that's just the "starting point". Note that in your Raw tab, for each Picture Style there are controls for Contrast, Saturation and Sharpening that you can play with to "optimize" those settings.
And then, you mention the results you get from bright, sunny, mid-day shots. Well, honestly, it's well-known that those are not optimal conditions for a lot of photography. And, in general, cameras struglle with scenes with bright light and shadows.
This is well known, and it should be noted that this is one of the strengths of shooting Raw, maybe you could consider it the "main" strength, at least I do, aside from the idea of "fixing" exposure problems and White Balance in your Raw processor.
So, DPP has the Hightlights and Shadows tools in the Raw tab which help you to recover those areas. It's something to work with. How to best/effectively work with those tools of course will depend on the scene and how you choose to expose it -- you may "push" your exposure "To The Right" so that you may actually want to pull your overall brightness back and then push up the shadows to compensate and the Highlights slider could get more "mileage" with your highlights. Or, you may decide to "expose for the highlights" which results in darker shadows, where in post-processing you'd need more emphasis in Shadow recover, maybe even needing to increase the overall Brightness and then really cranking down the Highlights slider and cranking up the Shadows slider.
Of course DPP has other tools, like the curves in both the Raw tab and the RGB tab that give you other ways of "playing" with your image. These are things to learn about as you go!
Well, anyway, those are my general thoughts!