Both aramid and carbon fiber have very high strength to weight ratios so they allow construction of a light canoe. Aramid has much better strength in tension than compression so it is best used for interior layers where the fibers will be stretched if the outer convex hull is indented.
Carbon fiber has a very high Young's modulus which means that it is very stiff, allowing for a highly efficient canoe as Kim said. An aramid/carbon canoe is very strong for its weight. The one disadvantage of carbon fiber is that when it fails it tends to fail catastrophically. And broken segments tend to have very sharp edges.
I agree mostly with pblanc above. Both Kevlar/Twaron and carbon also have very high stiffness to weight ratios, so they help with the weight reduction in canoes in that respect, also, in that less material is needed to have a stiff enough hull to not deform appreciably when paddling it.
If you're going to be very easy on the boat, it wouldn't matter which material or where it's put in the layup. For pure flatwater craft a pure carbon layup would be fine if care was taken when paddling to not hit much. The less deformation carbon gets, the better it does its job. The carbon on the outside and Kevlar on the inside is a good general strategy for a slightly more robust version. If you're going to be paddling whitewater or hitting a lot of rocks, or even sliding over logs, some compression will happen to the inside layer of the boat also (maybe not enough to matter?), and I have always put some glass in strategic spots as interior-most layer to take those stresses. I wouldn't bother on a hull meant primarily for flatwater. For that it's carbon and Kevlar.
For regular whitewater use The general layup with materials available to me at the time it was glass--preferrably S-glass--replacing the carbon as the outermost layer(s) to reduce the "catastrophic failure" issue pblanc mentions, which I totally agree with! A few layers of Kevlar/Twaron inside of that, and then some glass in the bilges (primarily the chines) of the hull. But that's me, not necessarily you.
My boatbuilding days were before Innegra was patented in 2006 (not really available until 2008?), so I've not had any experience with it, or with a few of the other newer reinforcing fabrics.
As to Blackfly's question in his original post, I think carbon and Kevlar (aramid) are entirely fine for maneuverable boats as long as they're not mistreated overly much, say used loaded with gear in multiday whitewater trips where bashing about is expected. Flatwater, even if bumping things occasionally, is fine. My opinion, not necessarily that of everyone (or anyone?)
