listen, i am on here to give legitimate advice that i know to be true based on my own experience and what i have learned on this forum. I also attempt to not give advice on something i don't know much about. Most people will tell you i am the first to respond to US/Canadian questions because i have almost 4 years dealing with crossing the border while dating and being married to my canadian. I am not going to tell you your plan is great when i know for sure you will have problems crossing with the facts you gave.
The fact remains you posted a question asking how you can move back to canada with a moving truck full of belongings and bring your wife, a us citizen who doesn't currently have a PR application in progress, with you. Most people on this forum who have traveled to and from us and canada with or without their spouse know this to be the biggest red flag that is subject to denial of entry. Even you pointed out the fact that the "stories" you read were similiar except for the fact those people did not bring a moving truck with every personal belonging they owned. Therefore, their situation is NOT the same as what you were asking. You seem to have realized bringing your stuff with you and your wife is not the best move. Great! I'm glad to have helped you figure that out!
I expressed my concern and my knowledge of this fact, and how others in your situation avoid issues at the border, ie: driving separately. It was met with what seemed to be arrogance in the belief that it's ridiculous to do such a thing, and as long as you are with her with her application for PR in your hand, she should be able to get in and stay there for an extended period of time of her choosing. If only it worked like that! I have also left out concerns about other things in your "plan" in an effort to not scare you because in my experience they are friendlier toward married couples than people just dating.
Considering, this thread has been read nearly 170 times, and I am the only one who has continued to write advice as to the risks of doing what you suggest most likely means people have read my responses, agree, and have nothing to add. QuebecOkie was kind enough to share her story that is similar to yours and gave some very great points that will help your wife travel with you across the border.
Bottom line is, there certainly is nothing wrong for a couple to travel across the border together. What is wrong is a US citizen expecting to cross the border and stay for an extended period of time without any proof of ties back to where they came from. The facts seem to be she will no longer have a residence or a job in the US when she attempts to cross with you. Again, another BIG RED FLAG! We can't just go and live with our spouses until the pr application is complete, and say i don't know when i plan to come back. We can certainly visit, and hope they let us in for 6 mo. when we ask, and apply for an extension to stay. As visitors we can not work or go to school, so this makes it difficult for many couples to take that route.
Truth is I don't know what's going to happen when you cross the border because as we all know it's always dependant on the border agent and their mood in that moment. All I can do is provide advice based on what i know, and what I know is your plan needs some work. Could you get someone who loves your plan and doesn't question when your wife plans to go back and lets her through for 6 mo.? sure you can! can you be greeted by someone at the end of their shift who has dealt with 100s of people telling the same sob story and chooses your wife as the one person to make the example of? you betcha!
This experience is very stressful, overwhelming and doesn't make sense at times. Unfortunately those are just facts we have to deal with in order to be with the ones we love. Wishing you and your wife lots of luck crossing the border. Would love to hear how easy peasy it is for you, because that gives me hope that it has the ability to get easier for the rest of us.