There isn't a perfectly straightforward answer here, but you do have a couple options. All of the best options involve orthodontics in my opinion. I too am missing my lateral incisors(what eventually inspired me to become a dentist!). 1. "Lateralization" of the canines is one option. It usually involves moving the canines into the space and reshaping them to look like laterals. You would still need some help orthodontically for this but could be the most simple at this point in your life and with the current position of the teeth. 2. Moving the canines out and making room for replacing the missing laterals either with dental implants or bridgework(the Maryland bridge is a more conservative technique that would be esthetically pleasing but not damage your other natural teeth if you could not immediately do implants). 3. You could do 6 veneers across your front teeth and basically mask the appearance and make it look like you have a central, lateral, and canine on each side with no spaces. Knowing which option is most appropriate is also very dependent on things like your bite, current X-rays, periodontal status, budget, etc. Hope this is helpful.
The answer to your question will not be able to be determined without an x-ray and a visit to the dentist. It will all depend on the severity of the decay within the tooth. The extent of the decay will dictate whether treatment can be as simple as a filling, require a crown, root canal & crown, or the tooth could need to be extracted and replaced. I would have it addressed as quickly as possible for best outcomes.
You're correct, a consultation with an orthodontist for braces or clear aligners is a great first step. Aside from the rotated canine you do have some other areas of improvement that could be made with orthodontic correction. A veneer is a possible option but could look large compared to the same tooth on the opposite side because of the difference in the size of the space on the right. It could require multiple veneers instead of a single veneer to look esthetically pleasing. Since all the teeth appear to be healthy otherwise, I would suggest beginning with the orthodontic consult. Composite bonding is also a possible more conservative alternative to a veneer if you decide against ortho but will have the same esthetic limitations.
