I have replaced the gunwales on 3 or 4 canoes with 3/4 X 3/4 and smaller size ash (rounded on the exposed edges) without any problems. I do both in and out wales at the same time. I start in the center with the stainless steel screws and using F clamps to hold the wood work my way out to the ends. It takes some pressure and it is a good idea to leave the gunwales long to provide a bit more leverage at the ends. So far I have not cracked a gunwale.

John VB