Actually, the idea of the possible wreck being a RAF B24 or some other lend-lease plane is not that far fetched, as starting from 1941 the RAF Ferry Command flew the planes to Dorval airport in Montreal prior to trans-atlantic ferry flights. Dorval is mere 100km away from Lake Simon.
Furthermore, based on junobeach.org, once the route was found successful the ferried planes were increasingly used to carry passengers, mail, and essential cargo such as medical or technical supplies, even ammunition.
The crew were civilians, it seems a bit difficult to find any info on the accidents enroute.
I'd consider feasible that if the supposed wreck was a civilian aircraft there would be some legacy info about the accident of such a large aircraft with many hands lost. Instead if it was a military aircraft on a ferry flight among thousands of ferry flights on same route in the midst of years of warfare, no one blinks an eye.