Many varnish manufacturers make varnish that has already been tinted. This saves a lot of time because you won't have to mix the stain and varnish or stain before varnishing. As with stains, these pre-tinted varnishes come in a variety of colors. When applying a pre-tinted varnish, you will notice that many of these products tend to cover up wood grain rather than enhancing it, which can give the wood a more painted look.
If you want to enhance the maple grain with a colored stain, apply it before varnishing. With maple, which doesn't have a very pronounced grain, stick with very light colors, such as caramel, to help bring out the darker streaks in the grain without completely obscuring the wood's natural highlights. Once the stain has been applied, you can apply a clear varnish to keep the floor protected. Stick with water-based products when working with maple.
An untinted oil-based varnish can actually do wonders for bare maple wood without the use of any sort of staining agent. Oil-based varnish and polyurethane turn a very warm amber color as they dry, which give wood a warm, oiled appearance while slightly enhancing the grain. After sanding the floor down, consider applying just a few coats of clear oil-based varnish without using wood stain. Try this method on a piece of scrap maple to determine whether you like it.
If you still prefer to finish your maple floors with a single application, avoid tinted varnishes and mix your own stain and varnish. Remember that the products must be compatible -- don't mix oil- and water-based products together. As with staining before varnishing, stick with water-based products for this method because the varnish will alter the appearance of the wood, even with the stain. When mixing the stain in the varnish, use about 1 to 2 ounces per gallon of varnish. Since the maple grain is easily overpowered by the stain, stick with the lower end of this range.