I have not been to martin falls or beyond but I have been to Thompson Manitoba and flown accross northern ontario and manitoba many times. When in the air it seems there is more water than land.

Also I live north of parry sound and have witnessed road building in the canadian shield on many occasions.

Currently they are 4 laning the road from parry sound to sudbury and fording many roads, rivers etc

Here we have lots of rock which they crush for fill when building roads.

I suspect that in the james bay lowlands there is less rock but I am told there is lots of gravel here and there....could easily be wrong.

I doubt if they truck in gravel etc....they will look for sources in the area

SN