Brakes should be done in pairs, i.e. both fronts and or both rears, never should you do just one corner of the vehicle, the pulling issue could be from new pads on one side and old pads on the other, improper/incomplete bleeding of the replaced caliper, or both, install the new pads on the other side and check again to make sure you bled all the air out the side with the new caliper and make sure you bed in the new pads properly for them to work as they should and then the pulling should be gone...unless the other caliper is not applying the same force as the new one, I always replace calipers in pairs as well even if only one seems to be needing to be replaced, the same applies to rotors and as mentioned pads.

By replacing any parts of the brakes in pairs you're insuring equal performance of the brakes from side to side, front to back is important to be working properly but it doesn't need to be balanced/equal as does side to side functionality of the brakes to insure straight braking.