I don't think I'm explaining my network properly. Check out this quick sketch:
I think I need to:
1) forward port 90 on the Shaw router to the "minifig" router
2) forward port 90 on "minifig" to the DVR
I know step #2 is functional because I can access the DVR from my phone when my phone is connected to the "minifig" network, using 192.168.1.12.
I think I have done step 1 correctly, based on this screenshot (while laptop is connected to shaw router):
I think I have minifig's external IP correct based on this screenshot (MAC address of minifig starts with C8D7):
Maybe there is something I'm missing between steps 1 and 2??