First National already has signage on the Exchange Tower. Tim's will probably have to wait until that agreement expires for a shot at putting their own branding on the building.
Once the private equity guys out of New York took over HBC, they moved everyone out of 401 Bay and split them between the Brampton office and a second location at Lawrence and Allen. It was an old data centre converted into additional office space and looks like the most depressing place in the world to work.
Now they just maintain a partial floor at the Simpson Tower more for ceremonial purposes. I think they have some board meetings there and maybe do the annual management call out of the location.