I'm considering buying a Lat FP for the value often discussed on this forum. I know it allows for SDC to an earlier flight. Can you use it to SDC to a later flight after a layover?
If not I'd stick to my flex fare strategy of booking the last option for the YYZ-YOW leg and then using standby to create the layover. Primarily interested in securing the J seat on the long leg, which would require booking a YYZ-YOW earlier than I'd like to leave there.

Example
AC 136 321 2020/03/18 07:40:00 2020/03/18 13:25:00 YYZ
AC 458 E90 2020/03/18 16:10:00 2020/03/18 17:11:00
Want to take AC464 or 464 at 19.10 or 20.10 instead of 458.