What's the best temporary solution for filling in a gap between my upper canine tooth and the first premolar? (photo)

I would recommend veneers, but since this is something that you definitely do not want, I would recommend getting bonding.  Bonding will accomplish the goal of closing the triangles and preventing cavities from invading.  However, if you get bonding, you can expect to need the dental...

You can achieve this look with bonding quite easily, and if you are ok with the proportions then go for it but it will make your two front teeth very large. 

A small gap between the two front teeth can be affordably and easily corrected by  composite bonding. Bondings can sometime discolor after a few years so you may have to have the procedure redone in the future.  Longterm options in the future could be to realign the teeth using...

You seem to have lost your trust and confidence in your dentist, thus maybe it is time to have a consultation with one or two COSMETIC dentists.  If the chip is minimal, generally a new direct composite bonding can be done to replace it and restore your tooth to the proper shape and color...

Absolutely.  Direct composite bonding is ideal for small spaces between any of the front six teeth either on the upper or lower arches.

If you had no tooth preparation (drilling) on your teeth before the direct composite bonding was placed, more than likely your orthodontist or cosmetic dentist will be able to remove it prior to starting your orthodontics.  I wouldn't be too concerned that you would have any decay under the...