If I cancel my Frame / Calendar Plus subscription before its expiration date, can it still remain active until the end of the year?

If you cancel your subscription, you won't have access to the Plus features until the end of your billing cycle, and you won't be charged further.

However, if your subscription was purchased through the Google Play or Apple App Store, you can pre-cancel, and you'll retain access to the subscription until its expiration without being charged for another year unless you reactivate it.