If the feds leave it up to the provinces, how will that not result in the same inequity of access as the abortion situation in law has?

Abortion is not illegal in Canada. It's covered by health legislation. Yet in some provinces and territories, and areas within them, it's impossible to access local legal health care abortions.

If cannabis is not illegal in Canada, and is covered by legislation, what's to stop provinces and territories, and areas within them, from blocking access in the same way?

Anything else, like basic justice, aside, this violates our universality principle.