Definate yes for lakers in diefenbaker, and they are huge, some guys I know lost one that stripped out all 35 lb test. They dont know if it was monster laker or rainbow. Thats actually how many of the 28+ rainbows have come out, fishing for lakers- wither thermoclaine or down rigging.
The popluation is not high by anymeans, the fish have trouble reproducing because of lack of rock and bigger yet, water fluctuations. Dep of Nat have made some mid water rock reefs in couteau bay and by quapelle dam, but not sure of success yet. As for lakers coming out from ice, never have heard of any- just spring and summer. I bet the quappelle dam might be a hot spot in the fall. The rock sure goes deep, and lota goldeye over there.
hope that helps. fishcrusher