I am having the same issue. Expansion and patch are both installed, I've tried changing zones, resting at the inn in Dyrford, and even starting Act II, but have not received any kind of letter. In my quest log underneath "The White March" it just says something like, "You have no leads". I am using a beta 2.0 save.
EDIT: Just tried opting back into the beta to see if it fixes the problem, and am now apparently running v1.0.5.0582 PX1 -steam. Wtf. Post-1.6 saves have disappeared, obviously. I'll opt back out of the beta and upload my save here.
You have to complete the Temple of Woedica (the first main story quest in Act II) to start the expansion.