Having received my trip documents (formerly known as the green book), I've been working on my Canadian entry documents and other requirements. Based on what I've learned, I'm passing on my information, especially since some of the Tauck information was misleading (out of date?). Be aware that all of this is subject to change and you should check the requirements for yourself.
Before Starting
Make sure you have an electronic copy of your vaccination card and passport (jpg, pdf, etc.). You will need to upload these when filling out the forms.
Provincial Requirements
These are the easiest. Follow the Tauck links to the websites for Nova Scotia and Prince Edward island (PEI). For PEI, Tauck (in the green book) says that you need to wait until you are within 14 days of arrival and that it can take up to 10 days to process. Neither of these statements is true, from my experience. I was able to submit the form a month in advance and received the approved e-mail in a few hours. You will need to know the date of your first day in PEI - check Day 5 in your green book. Nova Scotia is even easier. When your form is complete, you can print the final page as your registration form. They will also send it in an e-mail within 24 hours. There is no longer a entry requirement for New Brunswick.
Canadian Federal Requirments
These are more complicated. A checklist of requirements for vaccinated travelers can be found here:
https://travel.gc.ca/travel-covid/travel-restrictions/covid-vaccinated-travellers-entering-canada
As Tauck says, you need to use the ArriveCAN app or website to apply for entry. What they do not tell you is that you can only apply within 72 hours of your flight departure (the one that crosses the border, not any connecting flight in the US). Since I can't apply yet, my knowledge is limited at this time. Apparently, there is a $65 (US) fee per passenger, per Tauck. It appears that when done you will get a receipt to show at immigration. Not sure if this is e-mail, print the screen or what.
COVID Test
Be aware of the requirements for the COVID test. It must be done within 72 hours of your scheduled flight departure (again, the flight that enters Canada). Antigen tests are not accepted. Only molecular tests (PCR, NAAT, etc.) are accepted. Plan your test in advance. We leave on a Monday and plan to get a NAAT test with short turn around on Saturday afternoon (costing $199 each). We could get the free test at our pharmacy with a 2 day turnaround. However, with a Sunday in between that is just too risky for us. Also by getting it Saturday we will be covered if our flight is cancelled and we have to go the next day.
Quarantine Plan
Canada also requires you to submit a quarantine plan, should you test positive on arrival or fail to meet their requirements in some way on arrival. There is a quiz (take the "Assess your Quarantine Plan" link from the webpage referenced above). I told the quiz that I would stay in a hotel with my wife and order food for delivery. The quiz said that my plan was "likely considered suitable." I'm not sure if any more detail is required. I was hoping that Tauck would offer to some sort of assurance of a plan (like "our TD will arrange for your quarantine') or additional informaton. I've asked twice and was told they were looking into it, but so far it has dropped into a black hole.
I will post an update, if I get more information or anything changes. Again, I recommend that you look into this yourself and start as soon as you get your travel documents.