Hi Tom
Congratulations on your first project. Here's my opinion with the disclaimer that it's your canoe and you can do anything you want.
Fiberglass is a real bad idea. The goop is like frozen snot and it locks in moisture and ruins the wood under it. Also as an aside never let silicone get near your canoe either. If the canvas is off or will be coming off then you can do a backside rib repair or replacement. I've done both. A backside rib repair requires that tacks be removed from the area to get the planking off and that leaves holes in the ribs. That may or may not be an issue depending on your taste. When you put the planks back on it's impossible to put the tacks in the same hole. I suggest replacement. It's not that hard, even I can do it. There are about 60 tacks that hold planking to each rib. You wiggle out the tack with a tack puller being careful to twist it out the way it wants to come, that is, with the curl of the tack. You can feel it. But before you do that Make up the ribs you need and steam or boil them and bend them over the outside of the canoe about one or two ribs from the cracked one so that when it goes to the inside it'll fit. One or two ribs closer to the stem that is. Remove one rib at a time and replace it one at a time so's you don't get a lumpy canoe. Any minor marks on the outside of the canoe on the planking will be covered later by the canvas and the inside is of course new. As far as the stems are concerned you can cut back the bad wood and splice in some new. It's ok to use epoxy when splicing.
We like to see photos of projects as they go along so post on your project?
Good luck. Are you far from Flint area?