Your ordering is odd to me. Hanoi -> Can Tho -> back to Hanoi. It looks like Van Don has a new flight to Da Nang starting next month, so I'd go...
Hanoi, Lan Ha, fly to Danang for Hoi An, fly to Can Tho, bus to HCMC to fly to Siem Reap, then bus/fly to PP.
Your itinerary is very rushed (but it is possible as long as nothing goes wrong). I think you should skip Can Tho or Hoi An. Can Tho, to me, makes the most sense to skip mostly just due to the transportation factors.