I was trying to use a mifi (provides internet service to my laptop) in Canada, where 3G coverage for my phone was fine, but it did not work. Works fine in the US. I notice on the Verizon data service map all of Canada is listed as "Canada 3G". So is there any way I can get internet service in Canada using my existing device?
ANY time you travel outside of the US you need to CALL VZW CSR (800# or local number outside of US & Canada) and enable INTERNATIONAL ROAMING on your account.
This is for anti-fraud and security purposes.
The CSR will enable INTERNATIONAL CDMA roaming on your account so it can be used anywhere in the world /w CDMA coverage.
If your device supports GSM then it can be used in GSM only countries like Europe and that 3G roaming SIM card needs to be also activated by the CSR. (The SIM card has a serial# on the bottom of the card, this number will be activated by the VZW CSR. If you changed it by getting a NEW one from a VZW store or service the new SIM CARD SERIAL NUMBER (IMSI#) needs to be swapped to your account by the CSR).
It's denying you access AT THE MOMENT because the VZW international roaming system with Bell, Telus, MTS, and Sasktel is DENYING you coverage because your home account isn't activated.
Note that international roaming CAN BE EXPENSIVE and is NOT covered under ANY US domestic plan, see here:
Read the global data plans.
If you have a UNLOCKED GSM device (or get your VZW GLOBAL device unlocked or ATT/T-Mobile one unlocked /w the 850/1900 bands) you're better off buying a prepaid SIM card/chip for like $30 for 1-3GB of data instead.
As for the laptop device, next time you are on the NATIVE VZW network in the US do a *228, option 2 on the phone to update the roaming to the LATEST and the data stick in VZAccess Tools->Update roaming/PRL or something like that. I forgot.