In both cases, you should see a phugoid oscillation first. For a spam can that should be a small "roller coaster" in pitch repeating every 20-30 seconds or so.
If you use elevator to hold a fixed pitch, the oscillation will "damp", i.e. die away, very quickly indeed. If you are flying visually you should be doing this without even thinking about it.
If you don't touch the elevator, it still damps, but more slowly. The angle of attack stays pretty constant throughout the oscillation, but speed, pitch and height vary. Energy is swapped between kinetic and potential. (Yes, that E word again...)
After the oscillation?
Assuming you started at cruise speed (i.e. you start on the high speed side of the drag curve, and stay there):
With just extra power, and no other input except anti-yaw pedal, I would predict a gentle climb at a very slightly lower airspeed.
You need very slightly less lift because lift and thrust now share the task of opposing gravity.
You have the same angle of attack so you need slightly less speed.
Extra engine power with slightly lower drag losses means you climb.
With just some back-trim, and no other control input, I would expect a noticably lower airspeed, and a gentle climb.
Again you need very slightly less lift, and you have a higher angle of attack, so a lower speed is enough.
Lower speed means lower drag.
Same engine power with lower drag losses means you climb.