Gloss coated paper works perfectly for art posters. The colors look brighter and the coating gives the poster a nice shine. Coincidentally, UV coatings help protects artwork from moisture and adds durability to the paper, providing an extra layer of protection and adding to its longevity.
The biggest decision to make about your poster is which weight to use. You will also need to consider where your poster will be hanged. if you hang it outdoors, you will need a heavier stock and a UV coating to prevent fading. Heavier weights will last much longer in the outside elements and stay around longer. Usually, it is good to use 24# or 28# paper for posters. The larger the print, the heavier the paper should be so that it will be durable enough.