You don't. This is something covered under the US-Canada Tax Treaty and TurboTax does not support Tax Treaty claims or the required Tax Treaty Form 8833. The instructions in Pub 915 are the general instructions but they don't address all of the nuances including when you may need to file Form 8833.
If you want to use TurboTax online your best bet is don't report it and then if you get a notice from the IRS asking why, reply explaining that you are a Canadian resident and return Form 8833 with your reply.
If you want to file using TurboTax Desktop, override the taxable portion of social security, complete Form 8833 on your own, and print your return and mail it with the form attached.
