Ovechkin would've played on Canada's senior team for sure. Ovechkin's a special kind of young talent that only Eric Lindros has possessed for a long, long time. Other players of the past and/or the present may have more talent and offensive capability, like possibly Crosby for example, but only Lindros and Ovechkin have been able to combine this high level of skill with great size and physical domination at such a young age.
Ovechkin's 3-4 inches and 40-50 pounds on prospects like Crosby and Brule makes him the much more effective player against other men at this point in time. There really is no comparison. How effective would Crosby be if he received limited ice time against bigger, faster men while being expected to be a complete player first and not receiving the prime offensive ice time? Those are the things Team Canada would expect from any 18 year old forward, as they aren't going to put them on a scoring line, and Crosby isn't a good fit for the more defensive lines that Canada likes to match. Ovechkin is considerably stronger and more physical, has a more powerful stride, is better in his own zone, and can just basically do more away from the puck right now at this level of play. Ovechkin could play this role as well as nearly any Canadian forward out there, so even on a star laden Team Canada there is room for Ovechkin because he could sufficiently fit anywhere throughout the forward lines, whether scoring or checking.
Saying that Ovechkin's inclusion on Team Russia was only because of Russia's more liberal use of young players than Canada is pretty narrow minded. Fact is, nobody since Lindros (who played with the seniors at 18) has been this specific type of prospect, so trying to use Canada's prior selection history against him doesn't work.