For branded phones, the original carrier takes priority
unless you have a SIM card, in which case the SIM takes priority.
However, Verizon phones are special in that a SIM card will never take priority over original carrier (Verizon) because no other carrier puts out OS releases for Verizon phones as no other carrier sells the Verizon model of phones.
So if you want an OTA try this, if you haven't already: take out your Bell SIM card, and check for an update (over WiFi.) This may or may not work, but the idea behind doing this is that it will dissociate your phone from Bell while the SIM card is out. Don't worry about have to be in the US to get a Verizon update pushed to you, as people as far out as India have received updates on their Verizon branded phones (that they imported or whatever.) Also try Link.
But if are comfortable with other means of updating, you'll be able to get something off
Sachesi, or an
autoloader. The former is a non-destructive updating technique, while autoloaders are destructive in that they wipe your phone. The good thing is that Z30 models are all the same to Sachesi/autoloaders i.e. you don't have to worry about which carrier's update you're getting, or Z30 model#, etc.