Stain it and let dry real good and apply water based ploy. The wood conditioner is a good idea too on pine as it does stain unevenly. The conditioner will make the stain a bit lighter, but in the end you won't notice it. The water based poly will raise the grain some, so you may need to sand between coats, but it is more impervious to moisture than oil based when completely cured. Plus it is crystal clear, dry in about 2 hours and does not smell to the heavens.
If you are going to do the inside of the canopy and use MH lights, use the oil based spar (marine) poly as it has a VU protector in it, but it is a shade or two darker than regular oil poly.