I don't know the difference in bonding strength between brazing and epoxy, but I believe the mount in the attachment is meant to be brazed on...

A frame builder local to me advertizes brazing on items for $30, so assuming this counts a little extra, since it is 2 attachment points, let's say $50-$60... It might be worth the peace of mind to get it done right. Especially since the majority of braking power happens with the front brake...

However, if you can find someone who knows the properties of epoxy well enough to confirm that it is strong enough, and you pay attention to your preparation of the surfaces... then I would trust a good epoxy in this application.