I don't think this is true. Or rather, if it does indeed happen to be true, then I doubt it is because the Canadians are somehow inherently better at getting around their bias than other nations are. I think exposure is the key here. For hockey fans in Canada (and the USA too, let's not overlook that) the NHL is their top domestic league, so the vast majority of them follow the league regularly and pretty closely. I don't think there is less bias than in other nations, but the regular exposure tends to make it easier to realize when you were mistaken and wrong about a player. E.g. you might come in with a bias torwards your favourite Canadian defenceman, but when you see him not doing as well as you expected while a European defenceman you didn't think highly of keeps impressing you week after week, then chances are good you'll correct your original estimation.
Now of course, there are also hardcore NHL fans among hockey fans in Europe who follow the league just as closely. But for obvious reasons, this does not apply to the vast majority of hockey fans in Europe. For a broader part of the hockey-interested public there, news on the NHL often come in the form of reports soley focusing on the exploits of their local or regional or national heroes.
Mind you, while exposure often helps to correct bias, I don't think it necessarily works as well when players are really close in their level. When you've got a case like Bourque vs Lidström where a reasonable argument can be made for either player, a poll among Canadian fans (minus perhaps Detroit RW fans) would probably not be unbiased. But then, it would certainly be much less biased than a poll in Sweden on the same question.