Where on the Grand River? The K-W area is still shallow enough that you really want to go with a T-Formex or Royalex boat which wouldn't be the lightest for portaging. From around Paris on down river, then a composite should be fine. 

How big is the family? That will set the minimum size canoe that you are looking for. Given that you want to also use it for back country solo trips, you'll want a smaller tandem if possible.