Welcome to Cameralabs forums.
Regarding your questions, your Tamron lens should fit the D80 but be aware that since the D80 is not full frame, you should multiply the lens zoom range by 1.5 (by 1.6 in Canon 400D and 40D). This means that your lens will become equal to 42-450mm.
About the Cameras, in my opinion, the lines of Canon and Nikon are not the same. I think that the D80 is somewhere between the 400D and 40D, so you can compare it to both.
Canon EOS 50D, Canon EF 17-40L, Canon EF 70-200L f/4 IS and Canon SpeedLite 430EX