Will my natural teeth (bottom) ever be able to be whitened to match my veneers (top)? (Photo)

I agree with the suggestion of KOR whitening. It is the best on the market. If the KOR does not brighten your lower teeth as much as you would like, veneers would be the only other option.

The strongest whitening solution, which may be your only option without bottom veneers, would be KoR whitening. Search for it on RealSelf and you will find lots of information. It can be very expensive - $500-$1500. But it truly makes a huge difference and I think you will LOVE your smile after it. Average whitening options will most likely not get your bottom teeth white enough. Either way, as your teeth change with age, you will eventually most likely need veneers for the bottom. But if KoR works for you, that will at least not be for another 10 years!

It is always better to whiten first before doing veneers. That way you can match the veneers to the resulting shade of the opposing teeth. Since that did not happen, it is unlikely that you will be able to get the lowers to the same shade without doing veneers.

Based on your picture it is doubtful if your lower teeth will ever match your upper teeth exactly with bleaching alone. It is true that veneers can't be whitened. The best solution would have been to bleach your lower teeth before doing the veneers to determine exactly how white they could become. For a perfect match you will need to do lower veneers.