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My friend is in Jamaica and he is applying for a visitor visa and he still as a one entry valid visa for Canada is there a better chance of him getting his visitor visa approved? And if im financially supporting him for his 3 week stay and provide proof will he still have to provide his proof of funds for his stay?
If your friend already has a valid visitor visa he should not apply for another one.
If I’ve misunderstood and he needs a new visitor visa: he should provide both his proof of funds your letter saying you will support him, just to be safe.