I'm probably not the best person to give advice on this issue since I usually use the ol' "Kmart Blue Lite Specials", but since no one else has addressed this for you yet, I'll take a stab. It's been my general experience that tripods are like anything else...everyone seems to have their favorite and no single brand is really any better or worse than any other in a given price range.
Since you said you're looking to use this with one of those massive Canon chunks of glass (LOL!) obviously you're going to want something really stable as that's a lot of weight on the front of the camera. I think the biggest thing I would take into consideration is how and where you plan to use it. IF for example, you're primarily going to use it in a studio where you're not going to be dragging it around a lot, then I would suggest getting a big, beefy aluminum or even steel tripod since weight won't be that much of a consideration. If you're like me however and are going to be hauling that sucker around a lot, then you may wish to consider the carbon models. In my case, I tend to shoot at zoos and such and am usually hauling around all my crap for anywhere between 4-8 hours or more. Quite seriously, even though at 6'2" 220 lbs I'm a pretty big guy, just hauling my camera gear alone for that long gets really hard on the back and shoulders...hence why I use the light-weight cheapies. Since my biggest lens (at this point) is my Tamron 70-300mm on the front of a Rebel XT, I can get away without having anything "super duty". The nice thing I've noticed about the carbon fiber tripods is that while they are really heavy duty, they are much lighter comparatively speaking than their metal counterparts. Of course, they're also a lot more expensive!
I looked at a number of carbon tripods this last summer at a gear show I attended and they really seem to be quite stable. My only issue with them was simply price...for the $200+ that I could easily spend on one, at this point in my career I'd really rather put that investment into better lenses and such.
My suggestion would be to head to a local camera store and try a couple out yourself...beat the crap out of a sales person or two and see how well the tripod holds up! LOL!!! Seriously though, if you plan to be carrying your tripod around a lot, I'd really suggest going with carbon because of the weight factor. The little extra you pay for one can come out of the money that you would otherwise be spending on your chiropractor!
I hope this helps!