We're given to understand that these issues, running into persons who actually would be seen as presenting an excessive demand on health or social services, are extremely infrequent. I don't think the concerns you're suggesting are likely to manifest themselves. I don't think it's an issue at all, otherwise we would have seen it already.
I think the other point is that presumably the individuals who are chosen for immigration to Canada are chosen for a number of other reasons, and health is only one element of the whole picture. Presumably, there's actually a whole admissibility procedure that takes into consideration other elements. I think those are important as well. It's all a balance.