There are two parts in your question. I will try to answer this, but bear in mind that what I write is true about the EU and the standards in other parts of the world (e.g. USA) may not be quite so strict.
- Is the container safe?
- You shouldn't really worry about the metals leaking into the food. This sort of thing is regularly checked by the authorities. It is an analysis often performed in the lab I work at. Problems are extremely rare and they usually are damaged cans, broken or bent. So, take care if there is any evidence of damage.
- Bisphenol A in the lining. I am rather suspicious about this chemical but EFSA (European Food Safety Authority) have released a scientific evaluation on the chemical in 2015 and they think its OK:Canned salmon production line
- As for the fish. There are very strict standards about the fish to be used as raw material and about the end-products (again I'm talking about the EU). There are decomposition markers that are checked, for example histamine and TVN (total volatile nitrogen) and also controls for conservatives, heavy metals etc. Only rarely have we seen problems and in these cases I wouldn't have eaten the product anyway.
Anyway, it's still processed and conserved food, so a lot of nutritional elements have been
Canned tuna production linedegraded. Nothing beats fresh and I wouldn't base my diet on it but in the short/medium term it won't hurt you.