By the looks of those blisters in the paint, I'd say the separated brake bridge is a symptom of a larger rust issue. To answer the initial question - I'd avoid epoxy.
I would investigate the rust throughout the frame and determine whether the frame is worth salvaging before committing too much money to the project. It costs some (but not much) money to strip paint and treat the rust. If you have several spots that are rusted completely through the tubing, I personally would not want to ride it. On the other hand, if the rust is just scale and pitting, then an acid dip and a rattle can paintjob might be workable.
However, your total cost at that point may be more than the cost of simply finding a frame in better condition.