Hard to say- I'd be tempted to just do the main cabin and wait/hope for A to appear. But after a long haul in premium cabin I'm so tired it doesn't really seem to matter if I'm in F or Y- I sleep the last leg anyway.
You're looking at SEA-ANC for AS175 or AS121. Also AS735 should work, but expect schedule changes this far out (assuming you're connecting off CX858).
I'd also look at flying via LAX if using miles- see if there is space there. As there is saver (w, main cabin) on AS193 LAX-ANC. But you'd need to reroute your CX flight via LAX. Plus side, you might be able to get F

if it opens. CX F is my favorite long haul F product out there.
Last question: Would buying F on SEA-ANC allow you to requalify or qualify for a higher tier of status with Alaska?