I've done similar things to paddles using epoxy, splits in laminate & wood.  Epoxy sucks for sanding, so apply sparingly.  A little goes a long way.  Use the scraper, not a brush.

I like the West System kits that come with ketchup packets of epoxy & everything you need for a job like this.  The 101-6 from the below link.
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You might consider a strip of fibreglass along the paddle tip for extra durability.  If you do this, really soak the glass and then squish as much out as you can.  Clean up before it hardens.

Let the epoxy cure fully before putting any varnish on.  You can get amine blush.  Spar varnish, marine varnish.  If you go to a sailing shop they'll want to sell you white, not sure you want white so be specific if you want a clear finish.