What foods are contaminated with heavy metals and mercury?

What foods contain mercury or other heavy metals is going to depend wholly on where the food is coming from. A certain type of fish may have no mercury or be saturated depending on the waters it comes from. Similarly, a boxed food may have no heavy metals or it may be loaded depending on how that company processes the food. To know for sure, select a product of interest, find out the company that provides it, call the company and/or visit the website and discover their source or production method.
If there is contamination, they're going to want to cover it up if they can. Very rarely will anyone honestly say, "yes, my product has contamination." It's bad for business.
So, in other words, the best you can do is make an educated guess based on what they tell you and what their website says.
To be on the safe side, I don't recommend any canned foods. All canned foods will have some metal residue, and the chances are good that this residue is harmful to you. Canned foods also tend to contain table salt (not whole and good sea salt) as well as refined sweeteners. Also, nothing that comes in a can on a shelf is raw. It can't be raw on a shelf unless it is dehydrated or the shelf is refridgerated. Otherwise it would spoil.
Even if being "100% raw" is not a goal for you, I recommend avoiding canned food. If you have some organic canned chickpeas once a year, probably won't hurt you in the slightest, but don't make it your every day lunch.
To take things further, I generally don't recommend anything boxed at all. Anything advertising being "minute" (like minute rice) is a bad idea. So are artificial flavorings, colorings, MSG, refined sweeteners, etc. Boxed foods tend to have all of that, and they're way more likely to have heavy metals than fresh produce.
I do enjoy occasional raw organic vegan treats like Go Raw bars and Raw Crunch bars.
In addition, I ensure that I consume foods like cilantro in my meals and especially in my vegetable juices. Cilantro is a powerful heavy metal detoxifier. Its most effective when used in vegetable juice freshly made at home.

What foods are a good source of B-vitamins?

All fruits and leafy greens are excellent sources, and so are most other vegetables. Other categories of food (grains/seeds/nuts/beans/dairy/meat/eggs/fish) are all very limited in b-vitamins. In fact, most people become deficient in b-vitamins due to not getting enough variety of quantity of fresh fruits and leafy greens in their diet (with the exception of B12 which is entirely different from other b-vitamins and really more of a mineral than a vitamin anyway).
I have full charts for the various b-vitamins as well as the other vitamins and minerals (and protein, and the calcium to phosphorous ratio, and more) in my ultimate vitamin and mineral reference guide, Vitamin Confusion Solution.