H&D Walley13
It is true that a transducer does not shoot through foam care well at all but you can go around it.  NorthStar Bell canoes have a cut off diamond shaped foam core in the floor of the canoe.  I have a NorthStar Polaris Bell Magic with the same floor as the Northwind your Bell Magic and I mount the transducer behind the back seat just off of the foam core.  Works well. I use plumbers putty and it takes me about 10 minutes to switch it from one canoe to another. It sticks well enough that it has never fallen off in many trips to Canada and back but it is easy to remove to put in another canoe.
MP