Thank you for your question zuzu72.
I think the best answer to your question would be for you to go to a plastic surgeon or dermatologist and have them evaluate you. During that evaluation, you would have the opportunity to discuss how much larger you are looking for and what you feel makes you lips look slightly uneven. When it comes to lips, there are many options in regards to the technique and even the type of injectable to use. However, having that discussion with you in person would be the best way to clearly understand what you are looking for. The difference between a good injector and a great one is the ability to take your thoughts and create that into a result that satisfies what you are looking for.
As far as technique, you can use cannula to address this issue. However, when I have a patient like you that feels that their lips are asymmetric, I tend to avoid using a cannula because I think to make you happy I would need to make sure that I carefully address this asymmetry.
Depending on how much larger you want your lips would, for me, determine which filler to use. For patients who want subtle enlargement, I usually reach for Volbella. For the maximal effect, I usually reach for juvederm Ultra Plus. Between these 2 extremes, there are a whole hosts of other fillers to choose from.
I just think that you need to see a professional in your area in order to understand what you are looking for
Hope this helps,
All the best
Dr. Manios