Welcome to the Humminbird Side imaging Forums Adrian.
No you will not be able to do that with the 997 unit you have. To be able to share sonar, both units have to be Ethernet capable. Some of the current version units we now make are but not the older 997 unit.
The best that you could do would be to install a US3 Unit Switch and toggle the connection to the transducer on the back of the boat between unit, but both would not be able to display sonar at the same time. The issue with this is that the bow mounted unit would be showing you sonar data that was the length of your boat behind you.