HEHEHE, I just happened to have an expert in this area at my disposal :)

My dad and grandmother worked making tin cans for years. There is nothing harmful in a can. It may rust out in time and return some of the metals to the soil. But tin is a naturally occurring element. There are/were chemicals used for the old printed graphics on the can, but most cans now have paper labels on them. It is a relatively sanitary process, they keep the plant clean. If a sheet of tin falls on the floor, they do not put it back in th clean tin stack. And consider that most tin cans carry food in them that people eat. This is what my dad had to say...
"As for leaching...hmm...the metals are not necessarily harmful (did away with the baddie, lead, a long time ago...the coatings are all food apporved and baked onto the metal...the labels are not government approved (they are on the outside, right). The Restoleum? Uhm... If I were eating the flowers that grew from the bulbs I'd be concerned...All of our cans are baked in an oven (or UV'd) until they are stable (cured)...Rustoleum isn't...Your call on that one...but then again...miracle grow, weed and feed, et al... "
Hope this helps :)