The last line is very difficult. If you say "to open" or "to be opening" I'm given the impression that the tin opens up by itself. Am I wrong? The Swedish word implies that there's a person involved, someone that opens that tin, even if he/she is not mentioned.
I would personally agree with you. I see nothing wrong with "to be opened". The first verb in the sentence, "wants", is in the simple present tense, so there's no tense change going on there. Both of the suggested changes do indeed sound like the tin is opening itself.
