Both are silk-weaving traditions prized for weddings, but they come from different parts of India with distinct signatures.
Kanjivaram comes from Kanchipuram, Tamil Nadu, woven with a heavier silk and a contrast temple border. Banarasi comes from Varanasi, known for fine zari brocade woven into the body of the saree itself.
Kanjivaram has a bolder, more graphic border; Banarasi has an all-over intricate brocade pattern with a softer sheen.
Both suit weddings equally well — the choice usually comes down to family tradition and personal preference for border vs all-over brocade.