It might help to know why you want to move the plant (i.e., is it failing to thrive where it is or do workmen need quick access to the area?), but it can probably be done without harming the plant. Any move is stressful, though, so the stress may slow the plant's growth and bloom for a year or so after the move.

Camellia roots are mostly close to the surface, and a 3-year-old plant's root system is probably not too extensive, but if you do have some time to work with, it may be easier to move your camellia (and less stressful to the plant) if you start to prune the roots now in advance of a move in the fall.

If you don't have that much time before you need to relocate the plant, go ahead and do it ASAP, before (hopefully!) your plant has its annual growth spurt and puts out new foliage. An established camellia in the ground may need very little watering except during dry spells, but in a pot, you will need to monitor moisure to be sure it doesn't dry out.

Good luck!

Some camellia can actually have very deep root systems, for example the Camellia sinensis or tea plant can have a tap root that is 4 feet long. but if the plant was transplanted from a pot and not grown from seed in that spot chances are the tap root was cut before and is not very long. This causes the root system to be wide and shallower but still can be pretty big. Just look at it this way if the plant is 4feet tall it will probably have a root system to equally that in width or length to support all that plant.

Here is a link that might be useful: TheItalian Garden