Really any sealer/paint designed for exterior applications will work (and if you want clear, marine grade varnishes likely the most durable)–but like nearly everything that gets exposed to the elements, expect it to require maintenance & refinishing periodically… And using a filler or end grain sealer may be ideal on the edges–but not sure how that affects clear sealers…
But things like Gorilla Glue and cyanoacrylates are often used to finish and seal wood, so might be a quick & fairly easy treatment, too!
So it really depends on what end look you want. Lots of options will be painted, and narrower choices if stain/clear finish. And if you’re making something you want to last for a really long time, you may be better off using cedar or other species that has inherently better properties for exposure.