I won't offer an opinion on any part of the travel except the Alcan and Alaska...
As stated in the referenced thread, I think September is the best time of year in Alaska. If the choice was May/June or August/September, I'd choose August/September everyday. If weather is bad (particularly in September), it can be pretty dreary, but rainy May's and June's are not unknown (reference Los Anchorage this year, FWIW).
IMNSHO, the fall scenery (which includes mid-August onward, depending how far North one is) is better than Spring/Summer and, with some judicious planning, one can see as much wildlife...although possibly not the same type.
The body blow that bugs take in late August and the generally greater outflow than inflow of tourists in late August would really carry the day for me.