I think that option is mainly for financing. If you click the financing option it lets you go to the next page to get ready for preporder.View attachment 2260131
Looks like Apple.ca is now updated showing: "Choose your new iPhone today, then speed through checkout on 9.15. Pre‑order starting at 5:00 a.m. PT on 9.15."
In the Apple Store app, at the bottom is an option to "Save for later". To me, it seems like all this does is allow you to pre-order quicker on 9.15 without having to go through all the selections. Just immediately check out.
But if you click Buy outright it just lets you save.
So thats the best we can do, which is essentially like every other year it seems.