Can I add my wife as a dependent if I'm filing my own tax return?

You cannot claim your spouse as a dependent. You can apply for the Canada Caregiver Credit (CCC) for your spouse by going in each of your return in the menu on the left and click on INTRODUCTION then Contact info to answer the questions on the right side accordingly. You will answer to "Are you disabled" and the Canada Caregiver Amount Yes or No question.
When using the Easy Steps in our download version, this will enter the amount for you in Schedule 5 which you can view when you go into the Forms mode.

As per the Canada Revenue Agency (CRA) Line 30425 – Canada caregiver amount for spouse or common-law partner, or eligible dependant age 18 or older 

If you are eligible for the Canada caregiver amount for your spouse or common-law partner (see line 30300) or an eligible dependant 18 years of age or older (see line 30400), and their net income is between $8,021 and $26,782, you may be able to claim up to $7,999 on line 30425 of your return.

You must first claim $2,499 when calculating the spouse or common-law partner amount on line 30300 of your Schedule 5 or when calculating the amount for an eligible dependant on line 30400 of your Schedule 5, whichever applies. 

The Canada Revenue Agency (CRA) may ask for a signed statement from a medical practitioner showing when the impairment began and what its duration is expected to be.

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