I don't recall ever putting clear poly on cedar. I usually use it for outdoor things. At the same time, I never recall hearing of a problem with it. I have painted it with poly paints with no problem at all, so again, I doubt that there is any problem. WRC comes with one side rough and one side smooth for exterior usage. The rough side would be too rough for interior use where you can pick up splinters, etc.
One other thought is that if you can find a small sawmill doing hardwoods, you might actually be able to buy No.2 grade or pallet stock really cheaply. You do want to be sure that this has been kiln dried or throw it in the barn attic, or a place with good ventilation for 6 months or so. You want to stack the wood on stickers, 1x1 wood blocking, between the layers to keep the wood flat while it dries. You also want to do this in a place and time that the temperature of the wood will get up to 135 degrees for a couple of days to kill any bugs. The bugs will not like the dry wood inside a barn or the fact that it's a soft wood and will stay inside the hardwood until it gets too dry and hot for them to live.
When the wood is dry after 6 months of this, you can saw and mill it like the same $4/bdft stock from the home center but the cost will only be about $1/bdft. I pay $15 per pick-up truck load of shorts and firewood and get about a third of a pick-up truck load of good wood but about 3 foot long max. If I buy 400 bdft at a time of Select cherry or oak x 8-10' long, it's about $2/bdft but I have to dry it. I can get a better deal if the mill has more than they want on hand when I call to check availability. There are a lot of things like this that you can do if you can be creative, particularly if you have fun doing things like this.