A nice piece of tree ... an interesting talking point
As pine is a very porous wood there will be varying degrees of take-up of the finish you apply. I would suggest that you use a couple of coats of a sanding sealer before applying the finish.
If you choose a poly finish .. and that is what I would choose, be sure to apply it with a THIN coat (did I stress thin enough?). 3 thin coats will get you a much better finish than trying to put that much poly on the wood in one or two goes.
A LIGHT sand (240 or greater) between sanding ... some would use 0000 steel wool between coats )OK if not a water based poly)
A wipe on poly is thinned down poly and is easy to apply .. a brushed on poly needs a bit more skill but it isn't all that hard to learn.
Be sure to seal both sides, and the natural edge too. You may wish to use a 2 part resin to set the knot holes and fill the gaps/splits around the knots .. an extra step but it may be a good investment as the timber moves over the year.
I don't know of the manzanita wood .. Wikipedia say that its is "is also used as perches for
parrots and other large pet birds. and Manzanita wood, when dry, is excellent for burning in a
campfire,
barbecue,
fireplace, or
stove. It is dense and burns at a high temperature for long periods" If you choose a large multi stem piece then it might be worthwhile to use fixings that allow the top to move otherwise you may end up with cracking .. depends really on how big the support piece is .. a tree stump or an inverted branch will hve differing flex qualities.
Good work.
Be sure to post a pic of the finished job
Regards
Rob