Use the command qiime diversity beta-phylogenetic --help (EDIT: or qiime diversity beta-phylogenetic-alt --help) to see all available metrics.
Looks like weighted_normalized_unifrac is available in beta-phylogenetic-alt. not an available metric (I think this list may be based on qiime1, not qiime2).
weighted UniFrac is normalized (by even sampling) in QIIME2.
I hope that helps!