Don't need to spend $1000+ in order to do maps on the fly.
The 5" version of my new finder will do it for $449US.
You can also get it with Canadian lake charts.
You don't have to worry about a tablet getting wet, dying etc.
http://www.basspro.com/Garmin-EchoMAP-53CV-CHIRP-Fishfinder-and-Chartplotter-with-LakeV%C3%BC-HD-Maps/product/172504/