i'm by no means an expert but....
are you set on a poly finish? if not, what about a wet sanded danish oil finish? wet sanding with the oil will create a slurry of oil and wood to create a paste that will be the correct color and can fill whatever pores you need......
my steps doing this so far are:
sand 60 grit
rub in oil
let stand for a bit
wipe off oil
let dry (1 or more days)
repeated with 100, 150, 220 grits.......
then wet sand (oil) with 320 and 600 grit (already as smooth as h$%l)
note, this is NOT a glossy finish, but very satiny.
next step will be the watco satin wax and then Howard's carnuba/orange and beeswax
i'm using this method on a Jazz bass clone with a brazilian ash/flamed lauro canela body and a mighty mite maple/maple neck........yes my first is an "assembly" and i plan on working up to scratch builds as my confidence grows.........
i found this (or similar methods) online in various places.
otherwise i've had good luck using Minwax satin poly (wipe on) on a couple refinishes... i've had blotchy results with a cherry stain and that bass is on the list for the danish oil treatment....
anyways, HTH
jackie