When your back is turned your spectator places the dice into the small canister and remembers the number that is facing them upright. They then screw on the lid and place that canister into the bigger one and also screw up that lid!
Everything is seeled tight and there is no way anyone can see thru the canister. However you know exactly what number has been chosen.
Take a close look at the canister.s The lids are almost see thru. When the spectator has done everything you have asked them you casually show them the canister and as you are tipping it upside down and left and right you then TAKE THE PEEK and you can see the number they have chosen. Try it... It really is super cool and easy to obtain the chosen number.
Of course you must remember to act the part of a mind reading magician and use your magical powers to make this trick very believable!