Did your client physically perform any work in Canada during the period these stock options were vesting?
If he was a non-resident throughout the vesting period and did not work in Canada in 2025, his stock options are not subject to CPP.
TurboTax sees income in Box 14 but none in Box 16, implying that a deduction is missing.
Go to the T4 entry screen and check Box 28 (CPP/EI Exemption). If Box 26 (Pensionable Earnings) is not checked on your T4 slip, you may need to manually set it to $0. This informs the software that this specific income is not "pensionable," which resolves the error.
TurboTax is hard-coded to expect a Canadian province to calculate provincial tax. Since he is a non-resident, the "province" is actually a special CRA code.
In the Personal Profile, make sure the "Province of Residence on December 31" is set to "Non-Resident" (also known as "Outside Canada"). If the software forces a province for your US address, look for the code "ZZ" (Foreign/International) in the province dropdown. This is the standard CRA code for nonresidents. Nonresident returns cannot be filed electronically. You can always correct the address after printing it.
Hope this helps!
