Teeth whitening before marriage

Hello all, glad to announce that I am getting married to my high school sweet heart on this November. Preparations have started and I am really anxious. I started going to the gym and has managed to lose some considerable amount of weight. I am happy with my body right now and am trying to maintain it as such.

Now, I am concerned about my facial appearance. All of my friends commented that I have got an awkward smile. My teeth are stained too. I am totally unhappy about my smile. I want it to be fixed before the marriage. My fiance suggested having a teeth whitening procedure from a dental care centre in Toronto.

When should I have my teeth whitening done? I fear that my teeth will become yellowish again after the treatment? Is there any food items that should be avoided after having this treatment? Please give some genuine replies and suggestions. Thanks in advance.