Canada visitor visa based on invite letter from relative in USA

[IndianSupernova]

My employer is applying for my Canada work permit and I am likely to move to Canada in next 3-4 months. I want my parents to travel with me. However, they do not have a Canada visitor Visa. They have a US B2 Visa and have travelled to the US earlier to visit my uncle who lives in New York. If my uncle issues a letter inviting my parents to visit him for a family function in New York and states that he will also sponsor their trips to visit some tourist locations in Canada, will that be acceptable for granting Canada Visitor Visa? Or does the invite letter need to come from someone living in Canada?