The phone you are considering should work fine on Virgin Mobile Canada, since it supports both the 850MHz & 1900MHz HSPA bands. While their old network was CDMA based, they're now using HSPA (which is why your old phone worked as well).
As for those who claim it only works on Rogers, that does not make any sense unless they are in an area where Bell/Telus don't have HSPA service. For HSPA service, Rogers uses the same 850/1900MHz frequencies as Bell & Telus do, so as long as you are using the right APN and make sure the phone is set to "3G" it should work fine.
UPDATE: OK, I've seen this comment for other Blu phones as well, and I'm starting to wonder if it is indeed something with the baseband (radio) software they're using. I'm going out on a limb here, but the only thing I can think of is that it has an issue with Telus/Bell not actually having any 2G (GPRS/EDGE) support. Maybe see if you can contact Blu themselves first to see what they have to say on the matter.