My suggestion is only have the bags tagged to YYZ when you check in at your first destination. This will mean the PAX can claim his luggage in Canadian customs, exit the hall and not have to deal with the connecting PAX area (I dislike that area, it usually takes me longer) and then rent a car with GPS to go to either Woodbine or Square 1 for a few hrs, have a proper lunch or dinner and allow the family to roam around. Under a daily rate the car rental charge should be $40-65 which would likely be cheaper or comparable to taking taxi's both ways. This option also allows you to store your bags in the car.

When you return to YYZ proceed to the check in and have your bags tagged to the final destination. One important point about US pre-clearance is that if the PAX is a US citizen the line-ups are considerably shorter than the line for Cdn citizens thus saving a few more minutes of precious time to spend in the Outlying areas of T.O .

I have done this sort of connection a few times in YYZ when going onwards to a destination in the N.E USA but want to meet up with a family member for a few hrs and has worked seamlessly.

Is the PAX flying in to and out of YYZ T1?