What does CASL require that CAN-SPAM doesn’t?

The fundamental difference: CASL requires prior consent; CAN-SPAM doesn't. Under CAN-SPAM, you can email anyone a commercial message as long as you comply with disclosure requirements and honor unsubscribe requests. Under CASL, you need express or implied consent before sending-cold emailing without any prior relationship is prohibited.

CASL prohibits pre-checked consent boxes; CAN-SPAM has no position on how consent is obtained (it doesn't require consent at all). CASL requires specific sender identification including who is sending, on whose behalf, and valid contact information for 60 days; CAN-SPAM requires only a physical address and functional unsubscribe.

CASL's implied consent has time limits (24 months for purchases, 6 months for inquiries); CAN-SPAM has no concept of consent duration because it doesn't require consent. CASL penalties (up to $10M CAD) dramatically exceed CAN-SPAM penalties (~$50K USD). CASL is effectively opt-in with documentation requirements; CAN-SPAM is opt-out with minimal overhead. Treating them as equivalent standards leads to CASL violations.