I use the iCardio phone app and pair it with a Scosche Heart Rate Monitor which goes on your forearm not around your chest (much more comfortable) and a Vaaka Cadence Sensor for your paddle (stroke rate).
The app gives you speed, distance etc and can be set up to suit your requirements.
All works a treat and you can set the app up to give your km intervals, heart rate zones, voice feed back at particular intervals for a variety of data.
You really don't need to look down at your device to get feedback, it just talks you through it as you are going along. Keeps you company as well when you are paddling alone.
A big plus, of course is that you have a phone with you in case of an emergency.
For more info on these products go to
www.fitnesspaddlers.com.au