If you sand into the glass it w1ll start to appear white as you describe. It starts to show as a light weave and gets whiter the deeper you sand into it. It will still wet for you as you discovered. If it doesn't, try sanding it with a finer wet paper.

As you also now know, you have to be very careful on edges because you can take the epoxy away very quickly.

I wouldn't worry about and go to varnishing which will wet it out. If you fill it with epoxy, you create many days of work waiting for it to cure, re-sanding and trying to blend the patch etc. The canoe will be plenty strong and we'll wont tell anyone it's there.