Thanks sterling r for your help. I tried everything and still didn't work. Ended up setting up two separate Apple ID, one Canadian and one US, backed up all WhatsApp messages on iCloud, deleted the app and reintalled the app.
Now finally have WhatsApp again, but had lost a few days' worth of messages as back up only captured up to whato was initially set up at WhatsApp. I would suggest others to set up back up WhatsApp messages on a daily basis.
When I lost access to WhatsApp, I couldn't even go to WhatsApp settings to do the back up, the blank screen just said "This version of WhatsApp has expired. Please go to the App Store to update it." And when I got to App Store, "Your account is not valid for use in the Canadian store. You must switch to the US store before purchasing." And switching country didn't work! Going around in circle!