Would this be a valid routing for 144 TWOV?

Yes, this is eligible for 144 hour visa free transit valid for entire Guangdong province, but there is one huge but...

This but is related to the last segment because this segment cannot be done by train since there is no cross border railway line between mainland China and Macau and you need a ticket beforehand that you will really reach the third territory.

So, the solution, although a bit maybe inconvenient is to book a ferry ticket through TurboJet website from Shekou (in Shenzhen) to Macau. You are supposed to book this ticket even before you depart from Toronto and to print it out. You should have that printout at hand, ready to be presented in Toronto, Hong Kong and Guangzhou. Do not worry because ferry tickets are accepted. In the end, you really have to take exactly that ferry you have bought your ticket for.

When you reach Macau, you are free to go wherever you want, Hong Kong included.