@Boer
the 15 Day US Roaming add-on works just fine in Hawaii. You need a cellphone that's on the Public Mobile VoLTE whitelist in order to make calls...otherwise text and data work fine. The 3G refers to an amount of data while the 4G refers to download speeds.
added...you'll have a bucket of 3 GB's of data for your use with the add-on. If your plan in Canada is 4G (speed)...that's what you'll enjoy in USA too. Clipped from Help Files >> Subscriptions with 4G speed may reach download speeds of up to 100 Mbps
