Bon, "occasion" is French for "opportunity". But "opportunité" is rather rarely used in French. Je dirais presque que "opportunité" ne s'utilise que quand on parle du monde du travail ou de l'argent.

"Occasion" peut aussi avoir le sens de "événement", exemple "à l'occasion du nouvel an, je voyagerai". "Occasion à saisir" aura par contre le sens de "opportunité". Donc selon le contexte... Si tu as des phrases ou des exemples concrets, ce sera plus facile de déterminer le sens.

Their is a big difference between opportunity and occasion don't mistake them.Oppurtunity is advantageous circumstance like if you get a job and have an opportunity to go for it instead of dropping it, you can say kind of chance.Whereas,when it comes to occasion it's a particular event like you may say any festival, any moment which needed to be attended. Overall from my point of view both of them cannot be used as same because they make much difference in the sentence.