"Well, if you pick just one ton of waste from either plant it's the same waste!" is technically true, but it's neither here nor there.
(Of course in case of nuclear vs. coal it's a bit more complicated because the waste products are not the same, but I still think we can reasonably compare waste per energy.)
CANDU is a thermal water moderated reactor, albeit moderated with heavy water rather than light water, allowing it to use natural uranium instead of enriched (as Canada didn't have enrichment capability and didn't want to depend on other nations). And it's a pressure tube design, meaning the high pressure water is kept in a bunch of tubes rather than having one big pressure vessel like most light water reactors (again, because Canada didn't have heavy forges required to produce traditional reactor vessels).
What Bill Gates funded is a company called Terrapower that is making a sodium cooled fast breeder. Very different from CANDU. Fast breeders are a pretty cool concept, but they and the reprocessing technology for closing the fuel cycle isn't as mature as light water reactors.
I don't know why this isn't being pushed harder if it's safer and cleans up some of this waste.
CANDU reactors are Canadian, they use heavy water. They've been around for 50 years, people don't use them because they can't be used to make nuclear weapons. All the reators in Canada are these style.