A U Can Do 3D can in fact do some of the 3D maneuvers. The main reason it isn't an all-out 3D'er is the weight (wing loading).
There are only 3 engines I would consider for it.

I tend to prefer 4-strokes on 3D planes as they get the airframe moving quicker (not talking about top speed). If this was a 4-5 lb bird, it would be good on the .55AX.

1. OS 55AX 13x4 Xoar or APC sport. Would be just enough power.

2. Saito 82 14x6 Xoar or MAS S2. What I would recommend as a first four stroke for this plane.
You could also move this to a profile later on. (Easier to get the needles right than the YS)

3. YS 70 13x6 or 14x4. This is easily the most powerful of the three and would be my choice. It is not necessarily a good first time four stroke though.

Another consideration would be an OS 81 alpha but it's another 2 oz. heavier and every ounce counts.

Keep the stuff you add to it light. Be careful not to add weight to adjust CG. Get that right by motor placement after the other gear is in place.
Decent light servos for it are DS-821 Spektrum or JR on 6V.