I am sure there are numerous recipes for Belgium Waffles, even the Belgium Tourism Office has on their site recipes for traditional dishes inc. waffles, here is the link:
Belgian Tourist Office - official website - yWaffles
I have not checked this link, the one I sent you was highly recommended to me by a close friend that attended the Jacques Deseyne's culinary school. Let me know if you can read Flemish, I am sure she can provide other recipes.
There is nothing wrong with using Pancake mix and Canola oil. The important thing is to experiment and decide which one you like more. The butter for sure will provide more flavor (sometime adding a pinch of salt makes wonders).
Relative to the sparkling water, I use store brand making sure the bottle is fresh and stored horizontally. Since the CO2 is dissolved into the water under pressure, the longer the bottle stays on a shelf vertically, the less gas the water will have.