Euroflyer---Some of what you said I can verify is being correct, but I'm curious how you came up with these Seattle-Edmonton, and Anchorage to Vancouver flights?? Alaska doesn't serve either of those routes. Horizon flies F-28-4000s to Edmonton.
The 73Gs can be found between SEA-ANC, ANC-FAI, and ORD-ANC. The plane that flies to Chicago first goes SEA-ANC-FAI and on the way back flies ANC-FAI-SEA. Plus, there's another 73G in the SEA-ANC corridor. The 73G also flies to SNA frequently, and from LAX-SEA, PSP-SEA and SJC-PDX just to name a few routes. As new 73Gs continue to arrive, you will see them used a lot as spares.
MD-80s generally stay to the south in the winter, so I understand, they need a lot of de-icing fluid and just in general don't perform as well in cold weather. The 734s generally don't fly so much to Phoenix and Mexico because they don't do as well in very hot weather as the MD-80s. However, I imagine they don't have to cut-back loads on the 734s very often, because they do fly to Mexico, Las Vegas, Phoenix and Palm Springs. Due to noise restrictions, you never see MD-80s at SNA. Because Alaska operates a lot of SNA-OAK-SEA flights, you see fewer MD-80s at OAK. Also, Vancouver rarely gets MD-80s.
Alaska has three MD-80s with extended fuel tanks, which were delivered in the range of 1993-4. They were used for flights to Russia, and they are currently used on the two LAX-ANC flights and I think also on the SFO-ANC flight. In the winter, they are used for Seattle-Mexico non-stops.
As mentioned, the 737-200 Combis mainly stay in Alaska. There are 8, but Alaska hopes to get a 9th to improve reliability. They do come to SEA, for use on freighter flights, (flight numbers 800-900). I'm not sure if this was mentioned, but they often fly the "milk run," which is a flight from SEA-ANC that stops at most of the Panhandle towns.