I don't think you can activate them over the phone. You have to go to guest services. I'm not sure of the cost at that point, we didn't ask.
As a pp said, there is no benefit adding G+ for all days before. Just do it per day to be safe.
Note that the Canadian Tickets I am referring to are the ones from 2017 (ours were 4 day not sure if that was the only option) that show up in MDE with a 2030 expiry date. We had other Canadian "dated" tickets from August 2020 that don't show up in MDE anymore - These are just a credit in your account against a new purchase.