Usually users can switch their App Store region by logging out of their Apple ID for one region and then signing in with their Apple ID for the other region. All downloads will still remain on the iPhone and should not be erased. So why were your past purchases erased? Did you do this or did it just happen?
When app updates appear, the only updates you can download are for apps you downloaded with the Apple ID you're currently signed into. So this means having to regularly sign in and out of your Apple IDs.
This is what I mean. If you downloaded app X from the Indian store and you are signed in to the Apple ID for the Canadian store, the App Store app will still tell you that an update is available for app X. But downloading that update won't work unless you sign out of the Canadian Apple ID and then sign back into the Indian Apple ID. That's why it is better to just delete app X and redownload it using the Canadian ID as that meas it will be listed as a purchase for that ID. But if app X cost money then you don't want to do this because you don't want to pay for it again.
What you should do is delete any apps from the Indian store that are freebies and then download them again with your new Canadian Apple ID. This way you only have to change back to the old Indian Apple ID when you have to update an app that you paid for as you wouldn't want to have to pay for it again.
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