Sometimes this is a question of legislative drafting, but I don't think that's necessarily the case here.
In some cases, it's quite clear that one must proceed by section 44 of the Constitution Act, 1982, because one is seeking to amend textually the Constitution of Canada, that is, the Constitution Act. That is certainly the case with Bill C-19. It would effect an amendment to the very text of the Constitution Act, 1867.
In this particular case, first of all, our view is that this is not a constitutional amendment in the sense in which that is understood in the amending formula. That is, it does not purport to amend a provision of the Constitution of Canada. What it does do is take the provisions of the Constitution as a given--the formal appointing process, the summoning of senators by the Governor General, and the conventional role played by the Prime Minister--and provides a mechanism or a process by which the democratic principle can play on that choice of senators. So it is not proceeding via section 44 of the Constitution Act, 1982.
Some would argue that any organic legislation is, in a sense, constitutional in a small c sense. It's all part of the common law Constitution, if you will. And there are many statutes, including the Parliament of Canada Act, that have that organic character. But this is not, as I say, a constitutional amendment the way Bill C-19 is.