Understand that you want to go to YUL direct as much as possible, but I also agree nearby locations would be easier - specially those with a large oneworld presence such as NYC, ORD, BOS. You can then get separate flights into YUL and still get your car and all that. Though it seems YOW may also suit since you mention Ottawa? AC's Canada dominance means you're going to be very limited for options directly into Montreal.
I'm also very confused why you would look at routings involving the other side of the planet ie LHR and DOH/HKG/KUL to get to North America. I understand direct routings are going to be very difficult to find specially with just a few months notice, but given your ages and not wanting to deal with the rigmarole do you REALLY want to be bouncing around Asia, the ME and UK (and adding huge surcharges eg APD) if you don't actually want to stay in any of those places? You only appear to want to go to YUL and SYD or am I missing something obvious here?
Reward space into YUL will no doubt be very limited to as tend to be much smaller guage aircraft and even single class flying in. Have you looked at, for example, the J/Y combo reward to NYC, DFW or ORD for example and then 2xY into YUL< or even paid tix on AC? Or QF SYD-YVR then purchase AC to YUL?
Finally why not break up the trip into international and domestic? For example look for SYD-Canada as rewards and you could do CNS-SYD-CNS as separate tix - either reward or revenue (I tink these would possibly be much easier to deal with) and reduce the complexity that way. It may cost a little more in points I understand, but I have the impression points balance is not the prime concern here.
My four cents worth.
good luck.