Can I bring cannabis from a legal US state into Canada (or vice versa)?

No, in either direction, regardless of legalization on either side.

• Entering Canada: importing cannabis is a federal offence under the Cannabis Act, with penalties up to 14 years imprisonment.
• Entering the US: cannabis is a federal Schedule I controlled substance regardless of state law. CBP enforces federal law at every border crossing. Possession at the border can result in seizure, denial of entry for the trip, and a permanent refusal record affecting future US travel.

The border is federal in both countries. Provincial / state legalization simply does not apply at customs. Don't risk it — even small amounts have led to multi-year denials of entry for travellers who declared honestly assuming legal protection.