Don't know about April but Azamara has a wonderful itinerary Hong Kong to Singapore stopping at both Hanoi and Saigon enroute Singapore. We did almost identical itinerary on Regent Seven Seas Mariner in 2005 and loved it.
Azamara Voyage | Azamara Club Cruises
"The test of a first rate intelligence is the ability to hold two opposed ideas in the mind at the same time and still retain the ability to function."
F Scott Fitzgerald
Seven Seas Voyager (30nts) - Dubai - Cape Town - Nov 14