I am in Turkey now, [connected both sentences with a comma] but sometimes [corrected spelling] I go to Toronto and stay there for long periods of time [instead of "a long time"]. My cousin [spelling fixed] lives [capital and tense] in Vancouver, [capital-comma] but [instead of "and"] we have never [spelling] visited each other in Canada. We have only visited together in Turkey where we met [instead of "only in Turkey we meet]. I want to invite him to Toonto. [instead of "ask them why have not come to Toronto? or when are you coming to toronto?] I would write or say to my cousin: Next time I am in Toronto, would you please come to visit me? I plan to be in Toronto next [include the time period you will be there] and would love for you to visit if you are available. Please let me know if you will be able to visit and when you think you would be there.

Hi, yes its correct to use come when you are inviting them while you are already in the country. You have made a few mistakes, I have fixed them below :) I am in Turkey at the moment but sometimes I go to Toronto and stay there for a long time. My cousin Lives in Vancouver and we have never visited each other in Canada, we have only met in Turkey. I want to ask them why they have not come to Toronto? or when are you coming to Toronto? - you can ask them either question above.