Assuming the MCAS issue is taken care of, why is the MAX 9 defacto gone? Within North America, UA/DL/AS all fly the 739s on coast to coast missions, profitably.
The MAX 9 order has already been deferred. That to me, is a telling sign that AC is not necessarily in love with them. Will they be converted to MAX 8s? 10s? Who knows, but if the Transat deal goes through, with 14 A321LRs coming in... one wonders. It just happens that there are 11 deferred MAX 9s on order. There's no doubt that such a merger would result in some consolidation, and I'd bet a beer that you'll never see MAX 9s in Air Canada colours. But you will see the 321LR.
A possible scenario: AC retires the older A32x in the Rouge fleet, and moves the MAX 8s over to Rouge (or whatever the AC LCC division will be called; my guess is that they'll keep the Transat brand alive somehow, it has good value in Quebec), and takes the 321s and 321LRs into mainline (and perhaps notches up the order). the A330s go over to the LCC side to replace the 767s; maybe retain a few in premium config for mainline. My count shows 16 332s at AT; they seat more than the 767s at Rouge and could easily replace the 25 or so Rouge 767s. Their 2 333s could go over to mainline.
An interesting question is what will happen to the winter leases at AT...
BTW La Presse is reporting that Quebec Premier François Legault, the cofounder of Air Transat, is favourable to the merger.