If the Senators ship out Brady I would anticipate they'd be looking at receiving the best young NHL ready blue chip piece in return, tack on a pick and maybe a small cap dump and I think that's a base for a potential deal. This is a team that needs youth and depth after squandering so many draft picks, but they'll still want a "name" they can point to if they're trading their captain.
Mason MacTavish keeps jumping out as a name that makes sense. Good pedigree, good development path, plays the way coaching/management want their team to play and as much as it shouldn't matter he's from 10 minutes away from the Sens home arena. If Brady is traded it's because he demanded it and management might be targeting someone that won't want out eventually.
Maybe Stankoven+ from Dallas? I doubt Johnston would be on the table and I don't think Bourque++ moves the needle enough. Obviously money might be tough to figure out in this specific deal.