cans are afaik mostly tin-coated iron/steel sheets*, using sheer tin is the exception - tin steins come to mind
most tin is probably use in solders and I agree with @kwhitefoot - I am not aware of a current tin shortage. the USGS lists a minimum 4.8^6 tonnes of economically minable tin. with the current production only 16 years of stock, but not all reserves can be quantified and more recycling will be interesting when the prices for mined tin climb
* hereabouts. aluminium cans are only used for beverages and not food stuff
