There are two main factors that set how easy or difficult a speaker is to drive, these are Speaker Sensitivity and Impedance. A speaker rated lower Ohms requires more current than a higher Ohm speaker. Similarly, a speaker with lower sensitivity requires more power to reach the same volume as a speaker with higher sensitivity.
Focal Kanta No.3's nominal impedance level is 8 Ohms but can go down to as low as 3.0 ohms. 8 Ohms is pretty much the standard impedance amongst stereo speakers and amplifiers so Focal Kanta No.3 is not considered a difficult to drive speaker from Impedance perspective.
Focal Kanta No.3 has a sensitivity of 91 dB. 91 dB of Focal Kanta No.3 is considered a high sensitivity compared to average stereo speaker which makes Kanta No.3 an easy to drive from Sensitivity perspective.
Read our detailed Focal Kanta No.3 Review