Again, through the chair, the reason you haven't heard about the Elton override is that it's only about a month old. The Prime Minister actually told me some time ago that he wanted to be sure that the House of Commons' supremacy would rule in the end, and in a struggle to find out how we might accomplish that, I had Senator Hugh Segal look up the British acts of parliament, 1911 to 1945. I've read some pretty boring stuff, but 48 pages of what the British tried to do with the House of Lords is enough to make you go brain-dead. So I went back to Dr. David Elton because he has been my chief mentor. We've had constitutional advisors across Canada, but Dr. Elton has been the first and the steadiest. So I went to him with the problem and after a couple or three weeks he came up with what's called the Elton override.
To answer your question specifically, the first vote would be a simple majority of the Senate. In other words, Ontario and Quebec could alone decide that the representatives from those two provinces could send it back to the House of Commons. And if the House wanted to pursue the bill and revote it, then the override becomes part of the Senate, not the House of Commons. In order to exercise the override, they have to show they have a majority of elected representatives from seven provinces out of 10, representing 50% of the population.
That's an override that is about as strong as you can get, but if you have a House of Commons that ignores an override like that, then the bill should probably fail.