Do all fortified foods contain cyanocobalamin or do some contain methyl or hydroxo, and which natural sources of b12, are the most bioavailable?

Most cyanocobalamin: No way of knowing if "all" have the cyano form but I believe virtually all have that form as it is the least expensive and most widely available. But methylcobalamin is the optimal form for supplementation- see http://tinyurl.com/h7scsna Some foods contain higher concentrations of B12 but the form found in food is hydoxycobalamin so all equally bioavailable. See http://tinyurl.com/j7npwg3