My Front Teeth are Different Lengths - What Are my Options?

Since you are only 21, I would not want to remove any more tooth structure than necessay. If the tooth is intact, except for the root canal, dental resin bonding may be a good solution. The tooth can be made to look natural and color can be corrected with the bonding or a walking bleach to lighten just the one tooth. A veneer or crown are options, but potentially more aggressive. Talk to your dentist about the many options you have.

Either a porcelain veneer or crown can be placed on your root canaled tooth, while the other middle tooth may be a good candidate for a very conservative veneer.  It's quite challenging to get the two middle teeth to match perfectly especially if one is much shorter and darker than the other one.  It's critical to have the two middle teeth be as close to twins to have a pleasing smile.  Also, you may want to consider bleaching first to have all of your teeth lighter and more uniform in color, which makes the match that much easier.