I think DMU's make more sense for this route.
If VIA had a fleet of DMUs, then maybe. An order of one (or two if you want a spare) custom DMUs approved for use on an active freight mainline line by TC, and then supporting the maintenance for that unique trainset would be rather costly. If part of a bigger, long distancer fleet replacement plan, then maybe, though I have a feeling that if that is approved (and that's a big if), the White River, Norther Quebec, and possibly the Skeena will end up using 3 car venture trainsets, similar to what ONR is planning on using. Optimally they would be modified slightly to have a baggage car of some type to handle things like canoes and other large items.
Wasn‘t there talk of replacing the RDCs with locohaul in the 2010s but there was a question over whether the White River wye was suitable to turn a consist?
Times have changed. Back in 2010, VIA's F40s were not geared for reverse operation (at speed) and VIAs coaches had all seats facing forward, so they needed to be turned. On top of that, there was no order to replace the corridor fleet, and the E&N (Victoria-Cortney) was still running with RDCs, so the equipment needed to replace the RDCs would have been harder to come by (unless the plan was to build up more Renaissance equipment).
6400hp to move 2-3 cars seems excessive.
From a pulling power perspective, definitely, but given the remoteness of the service, they may need it for redundancy. The HVAC system in the coaches receives power from the locomotive, and if it were to fail in the middle of winter, it would get very frosty inside. A second locomotive could, at a minimum, be used to keep everyone warm (or cool in the summer) until the train can be rescued. Granted the Northern Quebec trains only have a single locomotive north of Hervey, so maybe it is a risk that VIA would be willing to take.
Wonder if converting one or more F40s to NPCUs would be an option.
I'm sure it is theoretically possible, but it hardly seems worth it for 1 train that runs 3 times a week.