We (mu husband and myself) are driving to Canada (Windsor) next week from Detroit in order to fly to Europe.
My husband is on my ArriveCan.
He is coming back before me and then will be once again driving to Windsor a week later (alone) to pick me up.
We haven't used ArriveCan before this.
My question is how does he fill out the info 72 hours before his trip (if he's on my profile) and does he open a new App for himself?
For a couple travelling together, a single ArriveCAN submission for the two of you will suffice, but as you have realized, either one of you travelling alone will need to have your own account.
Your husband has a choice of two options. The first is that he download the app onto his mobile phone and set up his account there. Then he's all set for those times he enters Canada alone.
The second option is for him to simply go to the online webpage version and open his account