One Dark Front Tooth - Options?

This a very good question that you have posed.  First, you can certainly try internal bleaching to see if this resolves the problem.  My own experience is that it works about 70% of the time. There are several internal bleaching techniques.  If this is not an option, yes, a single veneer can be done and the underlying dark shade blocked out. Again, there are also many techniques to achieving exceptional results.  One of the best results seems to be to block out the dark tooth with an opaque composite then taking the impression for the veneer.  

The porcelain veneer will require a skilled cosmetic dentist to be able to match the color, shade, contours, and texture so that it will blend in with your natural teeth.  

Another thought, if you want whiter teeth, consider bleaching your teeth before doing the porcelain veneer.

A veneers is a thin piece of porcelain that is translucent, so light passes through it. It is not a good option for masking a dark tooth.

You could try internally bleaching the tooth after the root canal is completed. There is a small risk of root resorption with this procedure.

The other option is to place a crown over the tooth to block out the dark color. 

My material of preference is a zirconia/porcelain crown.

Matching ONE front tooth is about the most difficult challenge a dentist faces, even one with much cosmetic experience.  If it's also dark from trauma, it's that much harder!  I would usually recommend bleaching everything first, seeing how light you can get that tooth, and then doing an all porcelain veneer or crown, depending on the amount of tooth structure remaining.  I usually try to avoid placing a post if there is sufficient tooth structure left, as they tend to weaken the teeth.  This link shows a patient post-trauma where one porcelain veneer was done on the dark tooth after bleaching.