Chestnut typically used ash, white oak, and sometimes spruce for gunwales. If you are restoring the boat, you should use what was used originally. If you are not experienced in identifying wood, see if you know someone who is, or look for one of the identification books at the library. If you are just repairing the canoe, and don't care about originality, then any of the typical gunwale woods would be acceptible (including ash, white oak, mahogany, cherry, spruce, and even walnut). Folks typically use harder woods for outwales, reserving spruce for inwales (though spruce can be found as outwales as well).
From the photos, it does not appear that the outwales are that bad... If it were my boat, and barring damage or rot I can't see, I'd probably just work some epoxy into the loose scarf, clamp it, and call it done.
Rocker is a descriptive term that is supposed to describe the curvature of the hull along the keel line. For ballpark purposes, I measure it as the difference between the baseline that intersects the hull at the center station and the station as measured at 1 foot aft of the stem. It's a pretty meaningless descriptive though, because it doesn't tell you how the curvature is distributed along the length of the hull: some canoes are evenly curved along their length, others are flat for some distance, then curved, etc. There are better measures of hull shape (like block coefficient and prismatic coefficient), but they involve considerable work to derive. You'll see some descriptions like "no rocker", "moderate" rocker" and "high rocker" which can be helpful, just a little, if you've looked at a lot of canoes. In the absence of anything better, so you have something to compare, just give the height of the bottom of the hull (excluding the keel) off the baseline at 12" aft of the stem...
