The J-20 is designed for canards; unlike, say, a Su-35 where canards are optional features (adds a bit more high-alpha, improves maneuverability, but increases weight and reduces thrust), the J-20 MUST operate with canards due to the wing layout.
The only issue with the canards is that they're not properly aligned with the anhedral wings for stealth; the current alignment is beneficial in terms of aerodynamics, but tilting the canards downwards means they're coplanar with the opposite wing and thus reduce RCS somewhat.
It's just part of the J-20's trade-offs between performance, stealth, range, payload, and maneuverability.
