These are very different products in spite of their similarities. My summary:
24-70:
Pros: f/2.8. Great IQ. Seems to be preferred amongst wedding shooters.
Cons: Heavier. Couple of hundreds more with no IS.
24-105:
Pros: Great IQ. Lighter, cheaper. IS.
Cons: Slower f/4.0.
Some of the cons of the 24-105 are offset by the 5D's ability to use higher ISOs. I use this lens all the time in relatively low-light situations at ISO 1000+. Now, not weddings. (I did one years ago for a friend and would never do one again--I admire those of you that do--successfully.)
The conclusion is, I'd take the recommendations of those who do shoot weddings over mine, but I think either can be made to work.