They set fire to their truck, hoping to cover any sort of evidence there might be linking them to any crimes (these two are not CSI, they don’t know what traces of anything might be in or on their truck) or at least, delay any positive identification until they are far away. They take the Rav and head south and then east, keeping to northerly roads and smaller towns (Fairview, Cold Lake, Meadow Lake) and avoiding any big cities (Edmonton, Saskatoon). Through more bad, inexperienced decisions, they end up at the end of the road in northern Manitoba.
Now what? They can’t go back, those Band Constables will see them in Split Lake again and start getting suspicious. They need to go it on foot. Since burning the camper seemed to sort of work and no one knows they’re way off in Manitoba, they’ll burn the Rav too.
They grab what they can carry and follow the creek bed down to the river. They find the old aluminum boat, they pile in. The boat is shallow and the river is faster than it seems. Maybe they hit a rock or maybe they just capsize. They make it to shore with their most important items, their guns at the very least. Perhaps the rest of their stuff including the boat itself floats on downstream and washes up where it is eventually found. According to the mini-doc made by the Globe and Mail linked by
@KR72, the boat is found in what looks like a bit of an eddy where flotsam could get stuck.