It's important to understand that you should always use a helmet made and certified for the specific sport/activity you are planning. Even though the helmets might look similar, there are several differences that make a helmet more or less suitable for different sports/activities. We are very serious about our helmets, and this is why we strongly recommend that you always use a helmet intended for the specific area of use.
A ski/snowboard helmet is specifically designed to deal with impacts at a higher speed than kayak/canoe helmets, and most importantly it is designed to do this under totally different conditions (think freezing temps, etc). There are also different requirements for coverage among other things. Most importantly: A ski/snowboard helmet is not designed to be totally submerged or designed to deal with any corrosion that might occur while being exposed to water for a long period of time.
A kayak/canoe helmet on the other hand is designed to deal with water. This means that not only is there a requirement for the helmet being buoyant, but it also needs to deal with impacts when submerged. All materials are specifically designed to deal with water, both in terms of performance and durability.