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I know traditional link exchanges aren't very valuable and Google doesn't respect them as much, but what about 3-way link exchanges?

I'm trying to understand the deep context of how Google (and others) treat rel=canonical tags.

There are a few situations that becomes relevant to understand how it works (rather than just code and pray):

1. If we are 301 redirecting PageA, but PageB still has rel=canonical of the URL of PageA, will Google still have PageA as its index?  One reason may be, the URL of PageA is more attractive (URL friendly).
2. We want to know the "delta" of how much content does Google determine as "duplicate content" when Google chooses to use the rel=canonical instead of the natural URL.  I'm suspecting that people may be abusing this, creating a hundred variation of the same page but using one rel=canonical.
3. Some of our 301 redirect work is affected by this because the client doesn't want the new URLs indexed yet.
4. Some legacy CMS tracking/systems that generates funny URLs (it increments each time you make an edit.  So a url like PageA.php becomes PageA.php?version=2, this drives us nuts) is causing a lot of duplicate content - but their CMS sometimes does some wacky 301 forwards.  We need a temporary solution until we can fix the programming logic of the CMS.

If I had two pages:

PageA about Cats

PageB about Dogs

If PageA had a link rel=canonical to PageB, but the content is different, how would Google resolve this and what would users see if they searched "Cats" or "Dogs?"

If PageA 301 redirected to PageB, (no content in PageA since it's 301 redirected), how would Google resolve this and what would users see if they searched "Cats" or "Dogs?"