10% ethanol blends will not hurt any 2-stroke engine. Oxygenates of various chemistries have been used in gasoline in the states for over 20 years. Not sure about Canada, but I'd guess its the same there, but either way, the engine materials are designed for this. Its when you start to get around 20% ethanol that you have issues, and those are primarily related to the ethanol attacking the gaskets, seals, and hoses, not due to lean siezes or burning a piston. And yes, you change the stoichiometry if you add ethanol, but it isn't the same "lean" that we think about when we run pure gasoline lean and it can burn up pistons. The real issue with running lean is that the gas burns faster locally in the combustion chamber, due to the excess of available oxygen. This creats local hot spots, often right around the spark plug, and that is what burns your piston. The "lean" created by adding ethanol doesn't act the same way at low percentages of ethanol because the lower energy available from ethanol doesnt create as much heat and the blend has a different burn pattern. If you ran engines at much higher compressions, like 15:1, a lean ethanol mixture starts to act like a lean gasoline mixture. But at the compression ratios in snowmobiles, this effect is minimized.
Sorry for the techie post - just regurgitating some info from a couple classes in college...