How can I restore the lustre of a cedar strip canoe that’s covered in fiberglass?

The problem you’re having is common and easily remedied. The fiberglass wasn’t the only material used on the outside of your canoe. There was also a layer of marine varnish. This further seals the surface and provides a glossy appearance. Trouble is, this varnish also gets dull and worn over time because of abrasion and the effects of UV rays. You can re-establish that new canoe finish with two or three coats of marine spar varnish meant especially for use on boats. Before you apply it, however, give the canoe a light sanding with a quarter sheet finishing sander fitted with 120-grit sandpaper. This creates a slightly roughened surface that holds the new finish properly. Sanding also removes any loose flakes of varnish that may be peeling off. Marine spar varnish comes in satin and high-gloss formulations, depending on how shiny you want your canoe to be. The main thing is that it be rated to resist UV exposure.