Staining Maple is a real adventure. Here are some points.

1. If you are staining with pigment stains, you shouldn't sand to more
than 150 grit. You will get a better color build and it will be
somewhat more consistent.

2. Pigments always obscure the grain somewhat but that's the nature of
the beast.

3. The inverse effect is where softer material takes more color and
harder material rejects. I see this a lot in Pine but haven't stained
much Maple so not sure about how to deal with it.

4. On soft woods you can do super thined coat of lacquer or varnish
first. Minwax sells pre-stain conditioner. P.S. Let it dry completly
(ie 24 hrs) vs the instructions given on the can. Then you will get the
desired effect. However, this is always done for soft woods, never
heard of doing it on Hard Maple but you could try.

5. Dealing with a brushed Poly Varnish is a bit tough. A few tips.
- Use "Tipping": This is one last pass of the brush nearly
perpendicular to the srface of the piece with just the very tip of the
brush touching the surface. This pops bubbles and levels brush marks.
- Thin the mixture (ignore mfg's warnings if any). Mineral Spirits
for oil based, or water for water based. Thinner mixtures make bubble
pop easier.
- Sand out bubbles and dust nibs with 320 or 400. Do it wet, mineral
spirits with oil, water with water. I use a very wet sanding technique
and it really makes a difference. I pour the MS right out of the can
and keep thigs real wet. 10 times more effective than dry sanding.