What finish is on there now? Do you care if the top looks different than the rest in color, shade, or gloss? Just by sanding the top, you'll expose the very light wood which will take at least a few years to start to darken up, depending on the amount of UV light hitting it. Is it stained, or does it seem to have a natural maple look? A stain or finish different in any way than the rest of the table will affect appearance significantly if you don't plan to refinish the entire thing.
Maple is a very hard, closed-grain wood. It'll resist water and abuse pretty well on its own. It doesn't really need the protection of a polyurethane finish. What is your planned use for the table? I'm assuming as a dining or kitchen table. I'd probably do something like this:
1. Sand with random orbital sander. Start with 100 grit if there are blemishes, although you might need to go down to 80 or 60 if they are significant.
2. Sand with 100, 150, and 220 grits, carefully cleaning all dust before moving to next grit or before first coat of finish. Sand by hand with the grain using 220 grit.
3. Use a wipe-on oil finish, such as Watco Danish Oil, Tung Oil, or just plain old boiled linseed oil (don't boil it though!
) following directions for dry times and reapplications.
Polyurethane is very easy to mess up while applying, and if it ever gets a blemish, you have to sand the whole piece down and do it over. Touch-ups will just change the blemish from one form to another. A traditional oil finish avoids the plastic look of polyurethane, and retains the real wood look and feel. Future blemishes can be sanded in small spots or sections, and then re-coated with the oil finish.
