There is no way to transfer or open TurboTax Canada Online returns in TurboTax Canada Desktop. TurboTax Online doesn't generate .ttxx files. 

Had I known that, I would not have bought the online version last year…

If you haven't used the product, you can submit an online refund request and purchase the TurboTax desktop version.

https://turbotax.community.intuit.ca/turbotax-support/en-ca/help-article/taxation/get-refund-turbota...